I think they get craftier with age.
My 23 yr old mare is still lightly worked but I'm constantly on the look out for signs that its time to hang up her bridle. In her youth she regularly spent her time either on her back legs or all four feet off the floor bronching (just to say I've had her since she was 5 and have explored every possible cause for this behaviour, vets, dentist, saddler, back lady and instructor all agree she just does it when excited and in particular loved to jump). Last week I thought the time had arrived, took her in the field and she dawdled round very disinterested in the whole thing, it was a sad day, I was very gentle and quiet and didn't push her at all. Decided today we'd have one more go but I thought a change of tact was worth a go. I egged her on with comments of 'are you ready Woody', 'lets go' pretty much how I would have as a kid then with lots more verbal encouragement turned her onto a straight and went into trot....except it wasn't, walk to canter, bucking, head in the air, ears as far forward as they could go. HHMMM think she's been conning me, also come to the conclusion perhaps she thought I was past it as I had been so boring recently, more 12 yr old kid riding required.
Wanted to share as although I was rather shakey about it all (rebuilding confidence after bad fall and broken back) I havn't stopped smiling since, life in the old girl yet!