Elway, Marino, and Montana were all 38 when they retired. Favre will be the same age in October.
After all the stuff that has transpired the past few days, I honestly don't see Brett playing past this season unless he absolutely feels this team is on the verge of a Super Bowl run in which, let's be honest here, probably is 2009 at the absolute soonest. If we show some great strides this season, I can see us contending for at least the division next year.
I don't think another year of sitting on the bench learning from Brett is going to hurt Rodgers either. If Brett retires after 2007, Rodgers will be entering the final year of his rookie contract then in '08, and if he doesn't show much in the way of being able to lead this football team, the Packers may not choose to renew his contract, although it usually takes more than one season to truly gauge a brand new QB, so it wouldn't suprise me if GB retained him beyond that unless he was absolutely terrible.