My motherhood

I've got 2 children ages 2 and 4. I'm 40. Sometimes I wonder what I was thinking. I wanted to be a mother so badly. Now I realize that when they're 10, I'll be over 50! When they're graduating high school, I'll be 60!! If they wait as long as I did to have kids, well, I may never see them. The other sad part of it all is that my husband and I have put on hold a lot of things we love to do: backpacking, rock climbing, and other physical activities. It's just too hard to do them with kids this small. So while we wait for them to be old enough to participate (or to spend some time with Grandma while we have fun) we're not getting any exercise and we turning into very large couch potatoes! By the time I can logistically do these kinds of things again, I may not physically be able to. I fear that I'm starting to get arthritis, so my joints may limit the kinds of things I can do.
I love my children and I wouldn't trade them for the world. But I need to somehow find myself outside of this label of stay-at-home mom.