I am over 25, albeit barely. I am not well-known, but I am published. Making money just about each day, yes, I do consider self-publishing to be a very legitimate way for an up and coming author to get a start. I doubt most musicians have made a name for themselves by 25 however, or that most comedians/actors/painters (ESPECIALLY fucking painters), and other artists have made names for themselves by 25. I mean, Christ, isn't there almost a curse with painters where often times they don't gain true recognition until they've fucking died? Of course there's some painters that gain notoriety while alive, but I hear most struggle along until they die and THEN might actually gain traction.
I don't feel like I wasted my potential. Sure, I could have started writing earlier, but then my books might not have been as good. Either way, half a decade isn't a long time in the grand scheme of things. As I stated, I'm not a well-known author, but I AM an author, and in spite of how briefly I've been an author I'm making money from my books. Not enough to make a living, but it's steadily growing, and I don't think it'll be much longer at the rate I'm going. I believe I'll be a full-time writer before I'm even 30 years old, and I have the blissful knowledge regarding the fact that, especially as a male, being 30 years old is still being a VERY young man, even still naive to an extent, and I'll have my ENTIRE fucking life ahead of me provided fate doesn't have a nasty surprise waiting. I specify as a male because by 30 years old, if a woman hasn't yet had a child, well... generally speaking, I think it's advised to get on that shit before the next decade is done, and even if another childless decade goes by they'd be VERY lucky to get a chance over the next couple years after that. So I can wait another 20+ years if I want before starting a family, if I ever decide to do so.
Mediocre? Technically, yeah. I'm new, I haven't written about all that much yet, I don't have much life experience... still, I think my books are good. Give it time, and I'll improve exponentially. Delusional? No. Optimistic? Bet your ass, I am. I don't know what you mean by 'past it', and as for embarrassed I guess to an extent I am. I write under a pseudonym; a pen name. I'm not yet comfortable with family knowing about the books I've written. Still if they found out, I think that would suck, but I wouldn't stop. I'd keep writing, self-publishing, and if they don't want to read some of the sex-bits or some of the extreme events in some of my books then they don't bloody well have to read them.
What about you, OP? Are you over 25, and if so, how would you answer all the questions you pose to us?