Donovan Dwyer is all of 8 years old — but he already plays guitar better than half of the “stars” on the pop charts. And this quart-sized Clapton plays a show at the Black Horse Pub in Park Slope every Wednesday night — and after you watch this stunning video of the pre-hormonal Hendrix, you’ll be heading out to that bar immediately. Reporter extraordinaire Joe Anuta brings you all the action from this underage axman.