I was also curious so I checked, the Penguins are the 13th youngest team going into next year at 27.4 years as the average age. The thing really pulling the average up is the fact that Letang, Malkin and Crosby are all in their mid 30s already, so I think that really emphasizes how good of a job JR has done this off-season to make the team younger. I don't have the exact numbers for last year, but being younger than average when your core is 33 or 34 seems like a pretty good thing for the rest of the team.
The only players older than the average age are Malkin (34), Crosby (33), Letang (33), Sceviour (31), Ruhwedel (30), DeSmith (29), Dumoulin (29), Zucker (28), Tanev (28) and Rust (28). The last 6 guys aren't even an age that I'd consider "old" for their positions, either. Guentzel, Kapanen, McCann, Jankowski, Blueger, Marino, Matheson, Pettersson and Jarry are all in the prime 23-26 age range, as are depth guys like Riikola, ZAR and Lafferty.