The comment was about who runs the senate, not the proposers.

Of the individuals you named, only Manchin has any chairmanships.

Nearly every single bill in Congress is introduced by non-chairmen, so this is an odd misdirection. Bills in both the entire session and in each subcommittee are voted on by members.

And again, this demonstrates that mocking old people as somehow the problem is factually unsupportable by the facts.

Again, “runs the senate.”

The process of bringing a bill to vote in committee or in session is not nearly as democratic as you imagine.