Centre backs usually get their breakthrough a few years after U21 level so its probably too early to say much about the current crop tbh. Theres not a lot of starting PL CBs aged 25 or less in general, regardless of nationality.
Oh yeah finalists in the International Intertoto Cup... something to remember.
I expect this game to be pretty dull. England defending - could have abused Alderweireld and Vertonghen turning slow as **** the last few years but Southgate seems more interested in 0-0 - and Belgium attacking...