Well there's always antidepressants and stimulants to help with that. In all seriousness, don't become a drug addict but if you're really worried about that there's a decent amount of research going on into improving brain plasticity so i wouldn't be surprised if there are drug treatments to "de-age" your brain in the near future.

That said, most of the "critical periods" for learning are over by the time you hit puberty and the ability to learn advanced knowledge, like the kind taught in college, doesn't decline that much with age so I wouldn't worry about it.