I've been road riding since '68 but didn't buy my first mountain bike until '88. Been riding both ever since, with the emphasis on the road . . . but still enjoying the mountain a lot!
My mountain bike is a hard-tail (aluminum) GT Zaskar LE with a SID fork, i.e. pretty much "old school" these days! Age wise, I'm 60.
So yes, go for it, you'll like it!
Rick / OCRR