Derg
I was told at 14 that I could not enter the RAF because I was a foreigner! Back in 1968. Just so happened that my Dad brought my Mom home from WW2. As did many others from all the Allies.
Well, my (Polish soldier) Dad came to England via Dunkirk in 1940, married a local girl (my Mum) in 1944 and remained in this country after the war. He didn't take out UK citizenship. Yet I was still able to join up as an RAF Apprentice in 1961 at age 16.
True I had to jump through hoops first though - do you remember the Form Ident 177? And throughout my 22 years service I still had to go for the occasional interview by the SIB, usually before a posting.
I'm sorry you were not able to enlist and can only assume it may be because you were still in contact with relatives in the old country at the time.
Polecat