One point that's probably been made before

I really wish retired players maintained their reputations. I can see basically no situation in which Steven Gerrard would be a "little-known English manager."

As a manager he has no reputation to begin with and has to work his way up.

You would still expect him to be well known, but the game calculates his reputation in terms of coaching experience and ability and as said before he has to work his way up

But it doesn't do it with everyone. Some players are instantly with national or continental experience. And ex-players don't actually have to work their way up anyway. There are loads of examples of this, but the first one that comes to mind is Gareth Southgate. Frank Rijkaard's first gig was as the Netherlands manager. And so on.

Alan Shearer, Paul Ince, Tony Adams. Less fortunate examples, but still. I guess it all boils down to the proving-yourself-at-level-x-factor. It's applicable to you too, as a player. If you start with sunday league football experience, you can still take over Man U. That's a fundamental unrealistic part of the game, obviously. If you however manage to prove that you're not 100% rubbish at that level, your reputation will grow, to eventually match the level of a PL manager. Just like these previously mentioned players have had to prove themselves (which, ironically, they've had a hard time doing.) Ironically enough, these recently retired outfield players have collectively had a hard time proving that they're up to the challenge. Only ones i can think of who are remotely successful IRL are Steve Bruce and Stuart Pearce.