Yes I sort of ran myself out after doing one marathon. The next winter came, and I couldn't keep up the training. The next spring and Duathlon season came and I sort of quit doing them. I guess I'd just gone from age 35-39 to 40-45, too. A problem is that as the age categories get higher, the proportion of serious athletes tends to increase. (though, of course, unlike me, G'day is a serious athlete).
I guess after my marathon I did do a "Horror Hill 30K". Near Erbsville, of all places. Someone (knowledgeable spectator of some sort) actually commented on my plodding slow-and-steady pace.
But I remember sort of too, my first half-marathon done, after an 80+km bicycle ride. I hadn't really prepared for the running distance (probably up to about 10K runs), hoping long bicycle rides would see me through. But there's more than just aerobics involved, and about half-way through the half-marathon I sort of forgot how to run, and finished the event in a brisk walk. Feeling sort of odd at the finish. In a sort of robotic mode so that I couldn't even break into a jog to cross the finish line, but did my 4 to 5 mph stride all the way through the finishing "arena".
Actually, because of a tendency towards knee and foot problems, I needed to reduce my number of runs from recommendations; hardly ever running two days in a row. To train for my marathon, I basically used Galloway's 1984 book, with that modification. Having a group to run with at lunch helped a lot, too. And then alternating weekends were my builder-upper runs. (That is, the intervening weekends were the "easy" ones; "just a half-marathon").
~50 minute 10Ks, and sub-two hour half-marathon (apart from that first) were sort of my pace. My marathon was just over 4 hours because of an emergency serious bathroom break (ick).