Walker, who was himself compared to Roberto Carlos during this summer's European Under-21 Championships in Denmark, admitted it had been "a massive step up" to senior international level.
"You have to always concentrate. There are more experienced players. There are more dangerous players," he said.
"But the under-21s is a fantastic level as well and you have to have that experience coming up through there to get into the seniors.
"Thankfully, the gaffer Stuart Pearce gave me the opportunity to play there in the summer and I think I learnt a lot from that as well."
Walker said: "It's an exciting squad now. It's full of youngsters - me, Danny Welbeck, Phil Jones, Rodwell - the list goes on.
"We're all in the manager's thoughts and I hope we're there in the summer."
He added: "I just want to go out there and play football - what I enjoy doing.
"The rest can take care of itself. I need to keep playing club football and hopefully keep performing at club football and then we'll look towards the summer."