As a "forty-something" year old I found BtVS for the first time.  Actully worked backwards becoming a fan of DB in Bones and Christian Kane in Leverage, I first watched all the Angel DVD's (Which had both of these actors in it) and THEN watched the BtVS DVD's after that.  Although first an Angel (DB really) fan (and I still don't hate him) I am now a Spike fan all the way!