Ace Frehley Is Too Old for This Crap ... Doctors Warn

Ace Frehley can no longer rock and roll all night -- doctors orders.

TMZ has learned Frehley is back home resting after being rushed to the hospital Friday night for exhaustion and dehydration. The ex KISS guitarist was released Sunday night with one warning: slow down.

Docs told the 64-year-old he's in great shape for his age, but needs to stop running around like he's still 18. He was advised to arrange a less exhausting tour schedule.

We're told Frehley already clocked in a dozen shows this month -- and was shooting a music video in L.A. at the same time ... flying back and forth to play his East Coast dates. Fortunately, the Saturday gig he had to cancel was his last tour date.