The great thing about hockey is that most good players can continue well into their 30s at a high level.
In the NFL, once a player hits 30 it's like the countdown to a drop off has begun, for most players. Pretty much all positions besides QBs, who can go a little longer generally.
In the NHL I'd say that age doesn't strike till more like 33 or 35. Plus they generally start earlier.
So for a guy like Dan Girardi who is 28, in the NFL, it would be "this is his three year prime window, he has to win right now."
In the NHL.... well, Girardi could be here playing at a top-4 D level for another 7 seasons.
You'll find analysis is showing just the opposite, that hockey player's peaks are now younger, and players are not maintaining their level of play into their 30s.
Traditional thinking had players peaking at ~28, but statistical models are now showing this as 25/26. Take a look at the very unscientific, but interesting top 50 players list on TSN:
http://www.tsn.ca/nhl/feature/?id=81134
Featuring only 12 players 30 or over, look at the high number of players under 25 that are producing some noteworthy production.
Lastly, with Dan Girardi's physical and shot blocking ways, I'm hoping for a full season before major injuries derailing him, not counting on the possibility of 7 additional seasons.
Defensemen especially are now only as good as their footspeed and ability to recover. Darian Hatcher, Wade Redden, once exemplary defensemen. Once their skating couldn't keep up, were out of league (we'll see how Wade Redden 2.0 does).
This league is now about skating, and skating ability skews younger.