I am 64 and still do dirt, lot less than i used to, i also ride a 990 adv. I stay away from the tight stuff, sand especially, 990 being just too heavy, too much like hard work. It's a fun bike on fire trail's, using the throttle to steer the bike, as long as you don't over do it. If you have the euros, obvious thing to do is buying KTM 300 or the like, for a second bike. The 690 enduro r is really popular here, they're out of stock, due to demand. I never had a chance to ride it, but i rode the 690sm r , same bike with 17 wheels, what a riot of a bike! Wouldn't tour on it though. Your age matters fuck all, it's only a number. I've met people in their forties, that were going on 80's, and vice versa. There was thread in OC, about a 990 adv, as a first bike. In my opinion, if you were only to ride blacktop, it would be ok, it's an easy bike to ride, albeit high, as for dirt, i would not recomend it for a beginner, you could get into serious strife with it, a dirt bike putting out 100 neddie's, it could get tricky
Get a ride on the 690 enduro r, and tell us how you went, good luck mate!