Adult "re-rider" issue - am I really that out of shape?

YES highfeather! There is a Pony Club for Adults, it's called Horsemasters and it's a part of the Pony Club. Look up on the Pony Club site and check for locations near you. There are Horsemasters in most of the U.S. Here in the Southeast U.S. We are in the process of organizing a Horsemasters group now. I'm an older adult recently getting back into the saddle after more than 25 years and share all of your pains and frustrations. Happy Trails (and Trials) to you!

Some of the farms around here allow adult students to work off part of the lesson fees by mucking stalls, turning out horses, etc. I've done it a few times and it helps with the overall fitness issues as well. Not sure if that would work for you though, if you are trailering in for lessons.

I've started a few wacky - but cheap - ways to augment my lessons, particularly as I live in a city 45 minutes away from the nearest barn. I got an inexpensive pair of reins on ebay and practice proper hand position by walking my 2 dogs with a whip long ways in both hands and each dog on a rein. I think it also helps overall hand dexterity. My neighbors think I am nuts, but my dogs are wonderfully patient and just ignore my "cues". Additionally, I got a wooden saddle stand and a cheap saddle off Craigslist to practice my seat, posting and 2 point at home. This is a great way to try some of the exercises in books (e.g. Centered Riding) in a saddle. I purchased some decent leathers and irons for my "fake horse" that I use during lessons so that my stirrup length is consistent.