If you're asking if you are too heavy for him, I'd say no, assuming he's fit and well. If he's an averagely chunky/boned NF he should be absolutely fine carrying your weight or even someone heavier.

But if he's usually quite jolly and now is acting lethargic and not wanting to move forwards, at his age and with his health issues, I would be a bit worried something's wrong. Unless you are normally over paranoid, an owner's instinct that all is not well is usually correct, even if it's hard to identify exactly what (if only they could talk!) - it may simply be him lacking strength/fitness or if he's recently changed shape it could be saddle fit, but it might well be time for some health checks. You could start with back person/physio/dentist to rule out the cheaper issues to fix before getting vet out? Out of interest how is he in hand, is he totally sound on a hard surface and will he happily go forward on the lunge or loose in the school/field in a sustained/controlled way, not just when running away from something, without any signs of pain or stress? If the latter is a yes that would definitely point to saddle being the issue for me, but the only way to be sure is vet investigations unfortunately. You could possibly ask your vet about a bute trial just to see if he improves on it, if so then he's def feeling something somewhere?

Has he just started on Prascend? A known side effect is depression - it's sometimes called the pergolide veil. A little bit about it here on the Laminitis Trust website. www.thelaminitissite.org/articles/starting-pergolideprascend

Hope he picks up again soon.

In my experience Cushing can take it out of them. And older ponies 20s plus’s definitely need extra If ridden regularly to keep them ticking over. Is he fed. Could look into feeding him something like calm and conditioning bye Allan and page just to put that spring back in his step. Just because you mentioned about his top line. Also maybe he could do a weeks work and a week off and so on? X

Agree with PP about checking for problems like saddle fit, and enough feed to keep his energy levels up, but just a thought... I’ve been tempted a couple of times to slightly over rug my horse now he’s in his 20s, thinking he needs a bit of extra comfort in his old age, and he absolutely HATES it. If he’s too warm he will be in a foul mood, lazy, snappy, and awkward, he won’t go forward, won’t soften, won’t cooperate at gates etc - just behaves like he’s fed up of the whole riding game. If he wears a lighter rug, even if I’m worried he’ll be cold, he comes in full of beans and happy to engage and go forward.
If Cushings is affecting his coat growth, even if clipped, and if you’re rugging him slightly too heavily he might just be too hot and a bit fed up, if it turns out not to be a physical or tack fitting issue after checks.