Tiny, I can totally relate. I didn't even get into riding seriously until I was 40, and have felt I'm behind the 8ball all the way through. My brain knows what to do, but my now 45 year old body is very reluctant to execute the knowledge. I am still trying to get up to a division that many younger riders wouldn't waste their time in.
The upsides is, we understand we have limits. Sure it sucks on one hand that we know we can get hurt, but it is also what makes for wise choices and less chances of the getting hurt part occurring. When I look at people half my age, who already have bad backs, knees and other horse related injuries, I feel better about my later start and slower progress. I know that, when I finally get there, if I ever get there, I will do it safely.
That all being said, get a synthetic saddle for the sport horse. They are very hard to come out of even during the biggest spooks.
Oh yeah, the wine and cupcake always work too.
You just have to see your distance...you don't have to like it.