Interesting. At the risk of pissing you off, I would say the exact opposite.
A rookie, going from this first season to his second, gains a WEALTH of experience.
An aging vet, going from year 12 to year 13, learns almost nothing new (if he didn't learn it in 12 years, 13 ain't gonna help).
A rookie will lose no speed or quickness going from age 22 to 23.
An aging RB going from age 32 to 33 will lose quite a bit. Playing smart helps only to a degree, otherwise LdT, S. Alexander, D. Terrell, E. Smith, etc would still be playing, not to mention Walter Payton, Jim Brown, Franco Harris, OJ, Marcus Allen, etc etc etc
I'm all for having two older RBs on a team.One would be okay, but old RBs rarely make a whole season. But when you sign a former great RB for small money, it's a sign that he is past his prime. Get a year or two out of him, and get someone else. Better to let him go a year early than a year late.