Oh yeah its totally un-realistic. With the way regression works in All-Madden players like Jamaal Charles, Megatron, Tom Brady, or Brett Favre will never exist.
What would be best (if EA took 2 seconds to think about this) is every time a new player is generated for a Rookie Draft randomly assign them a "regression begins now" age. For some RB's it might be age 27, some sooner at age 25, some later at age 30. This regression age could be a hidden figure that we cannot see, so that way you dont really know at what age that young RB you drafted will begin to regress.
If they just did that, it would be SO much better.