1855 Born but RAF record gives Aug 1868 (it may have just been used to get accepted by the RAF)
The Irish GRO has him aged 65 as well as the press report.
1879 May 3. There is a Militia record of a John O'Mara, born Glenadad, Tipperary. Aged 18 years and 6 months, attesting to RGA militia. This man would appear to be too young as this points to a birth about 1860
1855 Born Tipperary from censuses could be him
1901 census Barrow St. Pembroke West, Dublin
1911 census living at Barrow St. Pembroke West, Dublin
1918 Jul 13. Enlisted as a Clerk
1920 Feb 13. Discharged
1920 Mar 13. Killed in a road accident in Dublin
Soldiers effect does not give NOK
former IFCP case now on CWGC: https://www.cwgc.org/find-records/find-war-dead/casualty-details/75453272/john-o-mara/