[J.A.K.]

I would say 2-3 would be optimal, with the understanding that "friend" means you are genuinely interested in their well-being. Over the past couple of years, 3 of my closest friends and I have tapered off the frequency of contact due to life and distance. I have one best friend locally that I am in contact with everyday.

I think it's natural that your circle shrinks as you get older and priorities and interests (for all concerned) shift. I think you are also more tolerant of certain idiosyncrasies when young and without much responsibility. When you are holding down a marriage, parenthood, paying bills, etc. you start culling the 24/7 clowny fun-guy types.