I have been riding for 40+ years, mostly hunter/jumpers and ex-race horses purchased to re-sell.
I always wanted to try endurance - ALWAYS - but I would be riding dressage or have a horse that I thought wasn't suitable or was running 20 K's or riding in cycling races, just didn't get around to it.
So when I got to be 60, I decided I was too old to ride anymore and bought several Welsh ponies to show and drive. I had one more pony than I had barn, so I took one 14.1 hand pony to Bev and Robert Hoogendyk's boarding facility just up the road from where I live. They are endurance riders. They were having all the fun. They said (politely) of course you aren't too old for endurance.
I started conditioning that pony, decided that would never work, road a couple of rides on a terrific Arab gelding that my grandson has taken over and am now planning to ride this season on either a Tennessee walker gelding or my standardbred - or both.
Just go ride. The folks are terrific and it's the most fun I ever had on a horse.