Well I'm 34 and trying to keep it alive... It is not an inexpensive endeavor like it used to be which certainly makes it more challenging for younger generations, and I am a fairly competent mechanic who's done an engine swap, brake system rebuild and cooling system rebuild on the car (with many lessons learned). Fabrication and rust are my two biggest hurdles because I don't have the time or talent and they cost a boatload to do. So I stick with bolt-ons and enjoy my car as a survivor until I have the time or money to take care of the small rust issues.
I think some cars, like Tri Fives and almost anything in the 60's and early 70's will endure. I think Model T's and that era will be as unpopular as they are today but will have their crowd. I think the 30's-50's cars will mostly become obscure save very interesting models.