raphael, I'm impressed by the great empathy, awareness, and sensitivity you are expressing toward your father. Might he enjoy joining this forum...? He may find great affirmation and validation in perusing the various topics and threads in this Gifted Adult forum and elsewhere... even if he chooses to remain a private person and not post.
My thought on approaching a delicate topic is that conversation is often well-received if one is sharing something of their own experience... in little easy-to-digest bite-size increments... rather than having a big talk. Whether choosing to share a resource one has come across, a snippet of conversation that resonated, an insight that recently occurred, or even a second-hand story of a friend-of-a-friend... anything that made a difference. If you have an interest in common... history, or music, or fishing, or airplanes, or cooking, or being Mr-Fixit around the house... any small-talk can be a conversation opener and springboard to segue into the planned sharing. If you share something, he may share something.
Before broaching the subject of a parent's path in life, be aware that for many parents embracing who they are
may be delayed or deferred indefinitely once a child is in the picture. Indeed, who they are
may be forever changed. The sense of duty and obligation to provide for the physical needs of children, and contribute to their spiritual, social, emotional, and mental health may be an overwhelming responsibility... taken on at a relatively young age. Prioritizing family may spur one on to demonstrate a strong work ethic and dedication to a job or career which is noticeably less than ideal and far removed from developing one's potential in other areas. Exploring various careers, or pursuing self-actualization may wait until one is an empty-nester... and may wait even longer if time/energy/health do not permit attention to concurrent projects and/or if funds do not permit early retirement. Sometimes dreams may provide important benefits of diversion and mental exercise even if they are not actively pursued. That said, being a parent can provide a sense of fulfillment, of doing meaningful work, of having an important role, of belonging... without which there can be a void which some may strive to fill by seeking meaningful work in a job or career.
I may have belabored my point, but it was not without intention: Prepare yourself to consider that your dad may have had (or still has) great hopes and dreams but these may have been set aside or put on hold for love of you (and siblings, if this applies). Don't be surprised if you learn he weighed his options and prioritized his resources toward meeting your needs to the best of his ability, rather than focusing on his own. Understand that it can take a lifetime to master one's feelings about the road not taken, even though one is sure they made the best decision, given the circumstances. Put another way, one may still experience bouts of negative thoughts/emotions such as defensiveness, regret, loss, inferiority, or failure, if perceived as being critiqued for not having developed certain neglected aspects of potential. Especially if pointed out by a child for whom the sacrifice was made, as it may sound as though the child is judging the parent as less-than for not being able to do it all, or is ungrateful... either of which may suggest the parent made the wrong choice, thereby adding insult to injury.
Neither of you ought to feel badly about deferred dreams; from his vantage point of years he can relish his dreams and yet feel proud for having prioritized family to the best of his ability, you can appreciate the sacrifice often made by parents. Even in having different life paths, goals, financial budgets, and timing, you can both affirm and validate each other.
Some old sayings:
1) Life is what happens to you while you are busy making other plans
2) Happiness is a choice.
3) Things turn out best for the people who make the best of the way things turn out.