Veronika,
It is fairly easy to see the dream is addressing your waking life experiences {something that is usual for someone who is younger than the mid-life years,a phase that normally begins at around 35, when dreams tend to focus on 'inner' aspects as well as the outer waking experiences}. But are there underlying reasons to why you chose an older man to have a relationship? Let's examine this old 'tree' and see if it leads to other possibilities.

First, what was the relationship with your father? Could it be one reason you chose an older man is he fills a void from early life, that wise aspect your father should have provided? Why is it you choose this one 'old tree'? Is there real 'magic' involved? Such magic in nature is not really magic at all but merely a fulfillment of the 'natural' desires and needs of the human psyche. The guide in your dream is masculine. Is the guide and the old tree this older man? He is a replacement for the father you never had? This is a relatively an easy question to answer.
Even so, he is filling a void, it doesn't mean it is a wrong choice. It may be he does fulfill such a void and that is what you truly need in your life, at this stage of life. If the answer to the question is a 'yes' then you will need to examine how strong the unconscious desire is in making this choice of an older man.

That may lead to another aspect of your choice, and a question of choices. Are you the type {the dream does suggest a personality that tends to rely on the masculine to obtain and sustain strength in your waking life} that tends to make wise choices or someone who makes wrong choices only later to regret them? If it is the later then I would examine the relationship with the older man in a deeper light. If it is the former his wisdom may support a wiser than usual masculine wisdom you possess {suggesting you possess a wiser masculine aspect than the norm for your age}.

It may be the wisdom aspect of your psyche is what is in play with the dream. Is the relationship filling a void of the 'wise' father figure and if so is it a fit with your true self {someone with a wiser than the norm masculine attitude that compliments who you are and supports not only your needs but his}. If it is merely fulfilling the void of a lost father relationship then you need to examine the relationship and perhaps pay attention to what your friends have to say. This would fit with a personality that tends to make the wrong choices {is this you?}. If the 'old tree' is both the man you are dating and also a wise animus then you are probably the personality type that tends to make wise choices. There should be a fit to one or the other.

Forests are often symbolic of transitions. Trees are symbolic of growth. The dream is probably addressing issues of personal growth and transitions in your waking life. Depending on your personality the phases would be related to what I have mentioned previously. If you possess a wiser than normal 'masculine wisdom' then that would probably be a focus of the dream, and related to the choice of the older man you are in a relationship. If you tend to make wrong choices, choices you tend to regret later on, then the old tree would more likely be a symbol for a need/desire to fill that void from early life. There would be good possibility the relationship with the older man could be another 'wrong choice' based on a need to fulfill what was not provided by your father {an easy question to answer if you examine the relationship with your father}. Look to your personality and determine which you are. Someone who possess a wise masculine that tends to make wise decisions or someone who is the opposite, lacking the masculine qualities needed to make those wise decisions {which could be a product of not having that proper father/daughter relationship in your formative years}. If you answer these two questions honestly then I believe you will be in a good position to see why you have chosen an older man to have a relationship.

There is that possibility the need to fulfill the void lacking from the father relationship would work with the older man, he filling that void. But it would likely be a 'choice' that doesn't turn out to be the fulfillment you seek in life, it being a temporal band aid for something much deeper. Again, the lack of an ability to make the right choices in life coming back to haunt you.

Let me put a personal perspective on the relationship with the older man that is outside the dream commentary. I recently celebrated my 62 second birthday and having been married three times but not have had been in a long term relationship for over 18 years, I look at the possibility of experience as my guide. As well as my true self and what I need and desire at this stage in life {having had the experience of sorting through the life long accumulated 'baggage' and sorted it all out}.
For me, entertaining the possibility of having a relationship with someone 34 years my junior is not likely. The age difference, the stages of life we are both experiencing, the current needs and desires of both, would be factors I would look to. This would reflect who I am, and in the case of the older man in your life, the same. How would I, and he, reconcile these major differences? For me the past experiences in life, the study of Jungian psychology and reconciliation of my own inner world would make such a choice with a younger woman most improbable. The difference would be too great.
Unless this 'imaginary' woman possessed a wisdom well beyond her age, as well as possessed a personality/psyche that required her to seek out an older man {in which I would have to thoroughly examine those aspects and see where they came from and where they may lead}. She would have to be in the same mindset as I thus making my position in most aspects in life the same as hers. I believe in equality and an relationship would be one of sharing those same things we both wish for, things that are similar and would likely work {with the experience of three failed marriages I know what doesn't work}. A 28 year old woman most likely would never be at that same place, or even close to it, than where I am at the age of 62 {although I don't look or act my age because of having engaged in a physical fitness routine for the past 32 years}. Not to say it is an impossibility. For someone like myself who does make physical fitness a lifestyle, someone younger would more likely match that aspect of life {at least in appearance}.

Note: To see what 30 plus years of physical fitness does for someone at the 'advanced' aged of 62 watch my video of playing basketball {on YouTube}. Besides advocating a sound mind and spirit I also tend to 'push' the importance of good physical health. The old adage of 'pay me or pay me later' is evident here. If I can do it anyone can.

This is something you may want to consider beyond your own motivations. What are his motivations? I have friend my age who still dates only much younger women. He has deep psychological problems. Not to say your guy does. But it is something you need to consider. If your personality type is of making bad choices, and his personality is not much better, you can see where that would lead. Disaster. Let's hope everything is positive in both psyches of the masculine old tree and the younger feminine lady engage in her own real life fairy-tale {Merlin}.

What could it be that is would be 'pulling you away' from the old tree? Your friends in your waking life, yes, that is a 'conscious' reality. But are there underlying aspects, unconscious motivators that could also be pulling you away? The dream is the 'wisdom' self, even for those who lack true wisdom in their waking life. Putting the 'pieces of the puzzle' that is the dream is the task at hand. But answering the questions I have proposed should also lead to answers. Being honest with yourself is important. Your future is before you. A person of my age, well my future is something different. Can you reconcile these differences? My heart hopes the answer is yes. My mind, and experience, requires me to look at things logically. At this stage of life the head is now above the heart and looking at what the soul. In my philosophy the soul is of both amour and bliss. My amour is my bliss and it is based more on the creative and spiritual, and less on the yearnings of the heart. But that is me.
The question is 'Who are you'? And who this older man in your life?

Jerry