I am 54, and found out is is NOT a good idea to ride a big heavy bike in the dirt, even at a reasonable pace.
Bones break very easy when you get older.
So I traded the dr650 (not a super heavy bike) in on a TW200 for a while, and went through swamps and mud holes, on a lighter lower slower bike.
I would like to get something light and smaller, like an xt225 or crf230, as the TW200 is different from a regular dirt bike.
My skills are just as good as ever, my eyesight is not, and the bones are fragile, but I still like speed.
I do not want to screw myself up so bad I can't ride anymore, I almost did that in my last crash, so I went mellow.