OK first off, why should the specific age of 30 be allowed to carry all this extra meaning? 30 is just 29 + 1 or one less than 31. There's nothing inherently significant about it. All it means is: [number of times the earth has gone around the sun since you were born] modulo [number of fingers you have] = 0. It's 11110 in binary, or 1E in hex. Not such a round number now, eh?
By the way, the time when you were born, from whence we counted world-revolutions just now, is not at all important either. Only about 1/365th of the world's population gives a shit. heh heh
I'm messing with you a little bit and yet I'm not. Keeping it light-hearted because really it doesn't matter. It's not something to take seriously. Life, I mean. Not serious. Count me 100% in favor of a new beginning, because those are cool and make for a great story someday. Also, sadly I think academia in general might be a lost cause at this point, arguably a waste of time, and certainly a whole big whoppin' pile o'bullshit and sacrifice, as you have so astutely realized.
I don't know if I'll end up in the minority in this thread but I think you should spend some time doing the things you missed out on. But I also think you should just work it into your normal routine. Don't like, go on a 3-week herpes-catching spree in New Orleans or something, just make time every day for something fun and social. If you're doing something that prevents you from having any free time at all, that thing is unustainable, as you have, again, so astutely realized.
If sex were excruciating and millions of years of evolution hadn't selected so strongly for wanting to mate with as many people as possible from as many different tribes or genetic lines as possible, I'd say yeah probably on your deathbed you'll be totally indifferent to all the kids and grandkids you spawned, all gathered around you, and instead be thinking fondly of your PhD and/or immensely regretting that you didn't finish one. Not bloodly likely. I think life is about human relationships basically. Although according to evolution, it's not even that: life is basically for mating, and everything else is extraneous, except to the degree that it helps you get laid. I said according to evolution, all right? jeez! Evolution is dumb. It all (life I mean, and especially mating, but both) is inherently kinda dumb. Sex is dumb but we, also, are somewhat dumb. Maybe your only purpose here is to pass on some genetic material. After that, maybe nobody gives a shit, so however you spend your time after your genes have deserted your sinking-ass ship, it had better be whatever you actually and truly want to do. Get as many PhDs as you want, but they're optional and should be something YOU enjoy doing.
I don't mean to make light too much. Well yes I do. But nonetheless I remember being a bit depressed when I hit 30. On the day itself my pals took me to a drag-queen show and they had a big closed-circuit TV screen showing close-ups of onstage action as well as occasionally people the queens would pick out from the crowd to pick on. Well of course my buddies told them it was my 30th birthday and they did sing for me, also snarkily offering condolences, thanks a lot, but that meant the camera, behind the crowd and slightly above, was pointed at me for a bit and there on the screen I saw the back of my head for the first time in a while, already going bald. FUUUUUUUUU...
Then a big recession hit, I lost my "big, important" job, suddenly had time to kill and basically kicked off about 5 years of, if you'll pardon me, eating so much goddamned pussy that I barely had time for chores. Yes I'm a heterosexual male, my pronouns are (he, him, his penis). Such a thing is generally not compatible with being "in a relationship," but trust me, you're not "in" the relationship you're in, until you're so sick of hanging out with half-assed trollops, and so amazed to find a partner of quality, that you're actually relieved to be done with dating. Like there's not a trace of regret for the past because the present and future are so much better. That's where you want to be. That relationship will be the keeper. But oddly enough I think it'll have less to do with the relationship itself or the partner, and more to do with just your being ready for it yourself.