RFK Jr is the stealth moderate. The Dims are conceding that Trump’s policies are mega popular. So they have to move Trump away both by saying age is a factor and by also providing an alternative to Trump (or any other non-RINO) by presenting a seemingly sensible Dim RFK Jr. If the Dims thought their message was popular then RFK Jr’s message would sound more like Biden’s.
The party establishment doesn’t want Kennedy. The earth is more likely to spin backwards than they are to support him.
The DNC is already plotting to develop a way to count votes in NH and Iowa so RFK won’t even win the states biden is weak in.