It is very hard to pin down.
If you go by the age in 1901 of 26 that gives estimate DOB as: 31st March 1874 to 31st March 1875
Possible Births:
1. JOHN ROBINSON
Birth: 08 MAY 1874, , Ireland
Father: George Robinson
Mother: Catherine Noble
2. JOHN ROBINSON
Birth: 29 JUN 1874, , Ireland
Father: William Robinson
Mother: Eliza Johnston
3. JOHN ROBINSON
Birth: 20 SEP 1874 Civil, , , Ireland
Father: Thomas Robinson
Mother: Bridget Sexton
4. JOHN ROBINSON
Birth: 22 DEC 1874 Civil Registration, , , Ireland
Father: Arthur Robinson
Mother: Ellen McFarland
5. JOHN ROBINSON
Birth: 02 FEB 1875, , Ireland
Father: Edward Robinson
Mother: Maria Carroll
6. JOHN ROBINSON
Birth: 06 FEB 1875, , Ireland
Father: William Christie Robinson
Mother: Sarah Isabella Rowan Robinson
7. JOHN ROBINSON
Birth: 12 MAR 1875, , Ireland
Father: John Robinson
Mother: Margaret Noble Robinson
If you go by the age in 1911 of 39 that gives estimate DOB as 2nd April 1871 to 2nd April 1872
Possible Births:
1. JOHN ROBINSON
Birth: 22 AUG 1871, Antrim, Ireland
Father: JOHN ROBINSON
Mother: ELIZA JANE MCFADDEN
2. JOHN ROBINSON
Birth: 13 JAN 1872, , Ireland
Father: ANTHONY ROBINSON
Mother: ELLEN GOOD
3. JOHN ROBINSON
17 JAN 1872, , Ireland
Father: DANIEL ROBINSON
Mother: AGNES LISTER
Assuming that a least one of the ages he gave was correct the birth should be listed above. But making that assumption would not cover all bases if he was unsure of his DOB it may lay between the two! Sorry I could not help!