Thanks to both of you. I just wasn't sure that so late into the 1880's that people would be unsure...or as Craclyn said...lie about their ages.
It does happen. I have a great grandfather who dropped onto the planet in his mid-40s (possible name change) then gives a different age on each of the 5 subsequent documents for him. His reported birth year covers a span of 12 years since he lopped off 5 years each time he got married to be closer to the age of his bride 
I have a similar one whose wives were both more than a decade younger than him so he adjusted his age on records. Meanwhile, back home in Mayo, the ageing rates of his siblings speeded up. They were 20 years older in 1911 than they had been in 1901.
1911 census has him appearing to be younger than his younger sister. Calculating their mother's year of birth from her age on 1901 census results in a marriage age for her of around 10, which is obviously wrong. Ageing rate of eldest sister slowed between 1911 and her death 30 years later - age recorded at her death registration was at least 15 years less than her real age (whatever that was).
All members of that family were born prior to civil registration of births in Ireland (1864). I've found only 1 baptism out of 5 known children. The family were in the same parish for at least a century. Start date of surviving baptism registers is too late for the elder children. Some pages in a later register are illegible; unfortunately those pages include baptisms in the years when the youngest child was born.
Another pair of my Irish ancestors have questionable ages on English censuses. They might have been born in 1830s or 1840s. Their son's English wife was 2 -3 years older than him; she adjusted her age downwards.
Age discrepancies weren't confined to Irish-born people. An English ancestor, born 1822, had incorrect ages on almost every census, (she was more than a decade younger on one), except for 1891.
