In the British navy at one time Officers were allowed servants, according to rank they were allocated, a Captain could have up to four servants for every 100 men in the crew, an admiral 10 to 16. Other tasks such as boatswains, cooks, carpenters could all have servants according to the total number of crew.
For each servant they were given the pay of an ordinary seaman but were only obliged to pay one fifth to the servant, so using boys must have been attractive. If you wanted to earn some money, save being a drain on the family, going to sea as a young boy may have been more attractive as a servant than a full deckhand, so saying you were younger kept you off the main tasks but got you the experience and some money, just a thought, if a family started that way you can see why it may have been replicated,
Also of course I am not certain that birthdays, especially in the poorer families were really always celebrated, these days we get cards, "5 Today" and so on, in those days I am not sure it was the same. So if later on someone asked your age, on the spur of the moment if you are not 100 percent certain you can see how errors occurred and your answer may change according to the time of year and what period you wer born it. Just a few thoughts, could be miles off the track that is what came to my mind.
Anyone who knows the Walshes who emigrated to Moosejaw Canada between 1905 and 1914 I would love to make contact.
DW