If they are in perfect health/condition and you have checked with your vet! (I ride a mare in her late 20's and she loves jumping and actually jumps pretty high and we got approved to consistently jump her because she's healthy - so yes it's fine!)
If he is in perfect health (speak to a vet/chiro first) then sure but if they are around 30, I wouldn't be jumping them over high fences (under 1m10)
I used to ride a 31 year old throubread in jumpers and he was fine.
Um I would talk to your vet if they are in good health and have not serious hoof problems or back problems and you bet says it's ok then I'd go for it! Just make sure the horse with be ok.
Well it depends how their joints are doing I have a horse that's 20 and it's doing cross country fine .
I think it is ok as long as they are healthy and strong. I still compete with my 20yo horse in the 1,10m/1,15m classes and he is doing great!