Lighter pack weight! I do not think I would still be backpacking if the gear nowadays was like it was in the 1970's. I slowly convert to lighter stuff when the old gear wears out.

Moderate but every day exercise off season. I used to be a weekend warrior. Now I walk the dog 5 miles every day.

Avoid gaining weight. I am very disciplined about keeping my weight steady. If I want a desert or other goodie, I have to "earn it" before I eat it" with an equivalent calorie work out.

Save the joints! No longer running or doing activities that stress my joints. No heavy lifting or shoveling (had a bad spell of sciatica in my late 30's).

Go solo. Although some family members do not like this choice and it really is a bit safer in a group, I can go my own pace and stop and camp when I get a tweak in my knees or take a short day if I had a bad night's sleep.

Found alternate activity to pushing long mile days;fishing! And it also supplements my food so I can take less.

PS, am 70 this year. Do not notice much difference in abilities yet, knock on wood!