May I suggest you not set an age limit to your riding?
My first factory built horse trailer was a used 1949 Westerner, single axle. I bought a brand new Miley in 1976 - we were still seeing it on the road last summer, bright gold with Sturm Ranch Produce painted on the side in brown letters.
I started riding in 1963 at age 21. I followed endurance riding from it's inception with coverage of the first Tevis ride in Western Horseman. I was just always too busy with other types of horse "stuff" to get involved. I decided two years ago (age 62) that I'd probably better not wait much longer. I think my new horse should be ready for a 50 late this season or maybe next. I just got started, girl, won't be quitting at 65.