If, after a whole year together, a man in his 30s isn’t considering you and consulting you in his future plans, like where he’s applying to school and how you might navigate a potential long distance relationship, and he’s telling you that he’s attached but “the timing is wrong,” what he means is, if the situation were different and you were still you and he were still he and you met at a different place or time in your respective lives, he’d probably be all in, but right now he isn’t. He’s saying that where you both are now relative to where he wants to be five years from now doesn’t give him the luxury to put you and your relationship first, and his feelings for you, however strong they might be, are overshadowed by an ambition for something else — an ambition he has to put before you.
Medical school is all-encompassing. It doesn’t leave a lot of time or room for personal relationships. Your boyfriend probably knows this, or at least has a strong suspicion that this is the case, and it seems to me that he’s being as kind as he can by not committing to you when he knows — or strongly suspects — that over the course of the next many years he will not be able to be as present with you, both physically and mentally, as you might want or need.
You are not silly to ask whether your boyfriend sees you in his future. You want what you want, and you’d like the assurance that he wants the same thing. And he’s telling you that, right now, he can’t give you that assurance because what he wants most is something else — something that neither includes nor necessarily excludes you (but, frankly, won’t leave a lot of time for you). But you should understand that, if your boyfriend gets into medical school, it could potentially be years before he’s able to fully invest in your relationship. Only you can decide if his lack of commitment at this stage in your life and in your relationship is something you can deal with for the foreseeable future.
If you have a relationship/dating question I can help answer, you can send me your letters at firstname.lastname@example.org.