I play in a contract league with a cap on the number of total contract years we can have outstanding at any time (sort of a combination contract/salary cap)...you can find player ages on any stats site (profootballreference.com, nfl.com, yahoo.com, etc)...
As for strategies I generally try not to look too far ahead as our contracts are guaranteed (so a long contract to a bad player can cost you for a long time)...the longest I've ever granted was 4 years, as a lot can change in the NFL in 3 or 4 years...I try to stagger the expiration terms at the key position, for example I have a RB1 whose contract expires in 2007 and another that expires in 2009...this gives me time to restock the cupboard as it were...its also important to take a look at the contracts offered by other teams, noting in particular when key player contracts expire...by timing things right you can make sure you lose a key guy the same year several similar players from other teams become available on the open market...