I've been here on TRZ for a while, but tested the waters at CR back when I got into running last year. I very much appreciate the extreme competence of the management and commentators here (including Tinman, Ron and several other TRZ "old timers"), so this is where I hang most of the time.
My story is that I ran track in junior high, then drifted through competitive speed skating, cycling and dabbled in multi-sport for many years, before I came back to focus on running last year, so you you could say I had a 35 year layoff.
I'll put +1 on Ben's comments on recovery, I not only need more days in between workouts, I also need more warmup and cooldown than before. When I was racing bikes seriously (state AG TT champ in '96), I could ride hard as often as I wanted (usually 5-6 times per week), doing doubles four days a week, no warmup, no cooldown and felt just fine.
Ten years later, that ain't gonna happen no more! Every run has 1.5-2 miles warmup, 1.5-2 miles cooldown and I go easy 4 days a week, moderate on one and hard on two. I still end up with injuries to feet (mostly), lower leg (occasionally) and upper leg (rarely) more often than I should. I had a calf injury (peroneous longus tear at the origin) that gave me a six week layoff from running in April/May, during which I rode my bike (like a novice racer, 20-40 milers with some pretty hard days); this tired me out a lot more than it had 10-15 years ago.
At one+ year into running again, I can say that I can still go as hard as ever on hard days, but I need to make them much less frequent and with longer, easier intervals between those hard workouts.