Like you say, it's about getting that recovery right. I did a 10k this year and finished it in 57:26. To give some context my best is, I think, 56:30 and that was when I was 25/26. So in the space of ten years I've only lost 56 seconds.
But, fecking hell, two days later I couldn't get out of bed without my wife dragging me out. Even my balls hurt. I probably waited about three weeks before I went for even a ten minute jog. Whereas when I was 25/26 and ran the 10k I remember doing Tough Mudder the Saturday after, and running around on the Sunday taking photos of my then girlfriend's group who were doing the half race.
Tell me about it
. Can't even eat a single Toblerone triangle nowadays without my tits getting bigger.