His father (husb of Mary) was a fisherman and is absent from the 1851 - the census date usually corresponded with the start of the Kinsale fishery - however 7 or 8 is a little young to be on a fishing boat and his father appeared to be at home in 1861 - however there was a Thomas age 7 in the household, they had had a Thomas in 1837 who had died 1845, another in 1849 who died in 1851, so a 7 year Thomas doesn't fit - maybe this is your Allen ? - in 1871 he may well be old enough to go fishing ?