I've noticed that, as I get older, I've begun to cut back a bit on my backpacking. It's been several years since I've been out more than 3 nights, and I find myself tending to avoid places that are more than 6 or 7 hours' drive. I also find that I shoot for a couple less miles a day (say, 8 or 9 instead of 10 or 12.) Finally, I find that I tend to choose places where the elevation gains and losses aren't quite as large or steep as they used to be.
I'm doing this for a combination of reasons. One is that I prefer a small group to solo hiking, but have a lack of compatible hiking friends - I'm just not able to keep up the 2.5 mph pace, with no breaks, that the twenty-something set seems to prefer. (That may be changing; I've met some people my own age on some trips sponsored by a local outfitter; we've planned a couple of trips for ourselves.)
But ther are other reasons. Obviously, age and physical condition play a part; I just can't beat myself up like I once could. (Youth is indeed wasted on the young!) I've also got more work responsibilities than I once had (fortunately, our practice grew, so I'm not complaining - it bankrolls my gear addiction, but it also makes it harder to get away for more than a few days.
I'm now a grandpa, and those two granddaughters definitely have first claim to my free time. (I consider grandchildren as my best revenge.) As I age, I also find myself realizing that my wife, my children my friends, and even me, are mortal - I want to spend time with them, and they don't backpack.
I'm making an effort to increase the number of times I get out this year - I had cut back too far the last couple of years. However, I doubt I'll ever return to the 12-15 times a year, plus a week-long trip, that I used to schedule.
Anyone else noticing a change in their backpacking habits as they get older?