I know exactly what you are thinking. I am there too. Part of the time when I ride I am older than any 2 of the guys I ride with combined. I have always ride myself into shape. I am going to have to start working out pre season and loose some weight.
I am looking at mods to make the sled handle easier and allow me to get around easier. For me that's a 174 track, zbroz 36 arms, and pro motion over the next couple of seasons.
I am careful to conserve my energy and legs (have knee problems) as much as possible by setting down when I can. Take advantage of the things you do well. Old guys can read terrain and snow because that is how we got around 20 years ago when a 136 was a long track, 2 inch paddles were aftermarket and huge, and if you had 120 horse you were modded.
I find myself getting more winded every year, How old is to old for backcountry riding?
I'm turning 60, should I stop crying and exercise more?