Gave it up. I satisfied my curiosity as to how fast I could get as an old (45-48) guy. Put in just as many miles, if not more, than I did in my late teens / early 20s when I was serious. It takes too much time to continue indefinitely, and I no longer think it's healthy in those doses.
I can push my own limits in the weight room on 2 -3 hours / week instead of 10-12. I like to challenge myself, I don't much care *how*. :-)