well if you need D and you can trade Malkin or Stamkos for...hm...
Karlsson+Letang+Pietrangelo...I would consider it... if you cant get a package of those 3...what is highly unlikely...keep the two best FH players man ;)
try to grab one of those, they might come cheap and pay out big time
As you are virtually unbeatable on offence I'd keep them and look for some sleepers on D or a smart trade with depth plyaers for a top D-man. Regarding age you are in the driver's seat with Malkin an Stamkos in a keeper league.