The only really bad federal employees I've ever seen were retreads from Capitol Hill, or folks hired in by a new "appointed" Postmaster General from his old place of work, or from his friends, etc.
Some private sector folks just can't cut it in the federal environment. For some of them it's simply too much alcohol, or the requirement to show up every workday. Executive level people are like that.
Hogwash.
I’ve seen people appreciably older than 35 hired into my work places and they are/were utterly useless. Don’t even try to sell such nonsense. Age is no guarantee against incompetence. In private jobs they can and will get rid of such people.