I think that Luton had the least amount of goals conceded in League 2 when Walton was recalled. He did really well. He let in 6 goals in 7 games when on loan Southend and 26 in 27 for Luton.
He's too old and would have to be named in the 25 man squad.
This season players didn't need to be named in the squads if they were born on or after 1st Jan 1995, so logically next season will be 1st Jan 1996, Walton was born 9th November 1995.