Their 5th season all came when they were older than Rondo. If you can show that it's related only to number of years and not their ages you'd have something. Then again, if it's based on experience then you'd have to give a lot of weight to the jump Rondo made this year before the injuries struck, when he was leading the league in assists by a comfortable margin and among the MVP candidates.
I would definitely agree that years in the league, rather than age, is a much more pertinent number to look at, though I doubt the difference is enormous.
I suppose there may be some reason to think that Rondo might not have hit that "jump" season yet, since all of the other players you brought up (with the exception of Jason Kidd), played and developed for a longer time in college. I don't find that particularly persuasive, though.
If this last season should have been Rondo's jump year (as evidenced by his play at the beginning of the season), but was derailed by injuries, I understand the optimism and I don't disagree with it. I don't think it's unreasonable to suggest that Rondo's early-season level is close to his peak.
When he is healthy, we might see him sustain that kind of play for a season. However, without the sort of phenomenal supporting cast he had, he won't sniff anywhere close to 14-15 assists per game, and the Celtics won't have a top 2-3 record. That's the sort of player Rondo is -- give him a lot of really great weapons to use, and he'll "stir the drink." But I really don't think he's suited to being THE guy.
Rondo has a lot of similarities to John Stockton. Stockton needed Malone. Once the Big 3 retire, we either need to find Rondo a Malone, or we need to trade him so we can get a player who is more suited to being a two-way centerpiece.
I want to reiterate that I don't see this as a slight on Rondo as a player. It's just a recognition of the type of player that he is and the type of situations in which he will and will not succeed.