(Reference line is the first season of Rodriguez's current contract. Click here to enlarge)
A-Rod has the advantage in terms of WAR by age largely do to an extra season by age 21 (although it's only a 3 WAR difference), but if you look at WAR by season Pujols wins by a wide margin (17.3 WAR)--and that is over arguably the second or third most valuable player in recent history.
Bottom line: these players are very similar in terms of their sustained excellence by age 30 and within their first decade in the league, with the slight edge going to Pujols. Rodriguez has suffered a bit of a decline since signing his most recent contract (evident by the declining slope of his WAR at age 32/season 15), mostly due to injury and, likely, general ageing.
Pujols is looking for a 10-year deal, which would take him through age 41 and season 22. If he follows a similar path to A-Rod (just an assumption at this point) the slope of his WAR shouldn't start to dip until year four of that contract, two later than Rodriguez.
In terms of durability, there doesn't seem to be any clues to how Pujols will fair as he ages relative to A-Rod. Since 2001, Pujols has averaged 156 games per year. Prior to signing his latest extension, A-Rod averaged 153 (1994-2007). Both were very durable once becoming full-time starters. After the extension, however, A-Rod has only averaged 133 games per season.
Even if he begins his physical decline after the 2011 season, Pujols should retain his WAR better than A-Rod. Playing first instead of third or short will help, since a loss of footspeed, etc, will have less of an impact on his defense than someone like A-Rod.