Another here to say that it's no contest, the new stuff wins by a mile for technical trails.

If, however, you want to just ride some groomed fire trails, the old mtbs work fine. You can push them, but only so far. It becomes difficult to the point of unfun.

On the other hand, if you're a pro, you can ride anything and still shred. Still, notice the quite modern geometry of the frame- I doubt he'd fare as well with a bike from 1983.