I think as people age the only way they keep that social door open is by extending the interactions they have with a range of ages. By brother has good friends in their 60s and he's 30. You're spot on about time though, it's the one thing we'll all run out of some day. Better use all the time we have.
Yes, it's something that I began appreciating recently... Maybe is the "thirties crisis", who knows, but as I moved out from home and lived far away from my friends, who I meet almost every day, and then they had jobs and we meet every weekend... now I've realized that good relationships can and must endure through time, and we have to take care of it. I appreciate company, friendship and love now more than ever before.
I wish I had both friends in real life to get together with and more time in the day to finish stuff and to relax. Sigh.
They also both seem to become harder to find. I don't have the social energy for friends. I have the urge to block or avoid most people I come across. And I seem to be working, studying and sleeping and doing nothing else. I agree that both of these things are definitely valuable I just wish they were more easily available sometimes.