As I said looking at his WW1 record he enlisted in Mayo.
Family Search (IGI) has a submission by a church member for A Frizelle b 1890 - father John H Frizelle, Ballycastle.
http://www.mayomemorialpeacepark.org/the_wall/wall3.html has two Frizelles from WW1 who I thought may be yours. Commonwealth Graves site has
William Robert Frizelle born around 1875 -father is Robert of The Glen Ballycastle- surely related?
A Frizelle born 1890 - father -John H Frizelle, Ballinglen Ballycastle.
(same person as IGI) so that looks promising.
The 1901 census site -
http://www.leitrim-roscommon.com/1901census/ doesn't seem to have any Frizelle or variations around Ballycastle.
I have looked for Church of Ireland Ballycastle- much of Irish records is sparse at the best of times but I can't find any reference online.
If you are close to a Family Search library (Latter Day Saints (Mormon) Church) you can often access BMD indexes for Ireland so you could get George's birth record. Northern Ireland census would also be available there but I think that is only if you think that George was sent to a MacNeice (Bishop or otherwise there).
Will keep thinking.