Question about registering players (EPL)

Hello.

I'm so sorry if this has been asked before (I'm sure it will have been but you try searching 'registering' on these forums...!) but I've some questions about registering players in the EPL.

I registered 25 players at the start of the season. Now in Jan I've signed two players which I want to play, one is English, the other Chilean. Now, I've noticed that I've been playing a 17yr old Spanish striker for the first half the season who hasn't been registered (doesn't have a shirt number)... and now on the squad selection page the Chilean has Unr next to his name yet the Englishman doesn't.

Does the Englishman need registering then or can he play regardless without taking a shirt number? Or can just twenty-five players be registered and only they play? What are the rules regarding youth/home-grown players playing without being registered?

Can someone please explain how this works? I'm confused.

You only have to register players above 21 years of age, anybody younger can play without being registered

Oh I see.

I was confused because I just played them in the FA Cup without registering them but now see it's regarding the EPL purely.

Thanks.