Well, no, no way to affirm that, Onésime is 3 on 1871 census and 13 on 1881 census, so from that he would be born around 1868. Louis de Gonzague is actually a saint's name. Nothing awkward about it, no more than Onésime. Often kids with these long names just used the short form. Might have dies young, if you compare 1871 and 1881 censuses, there's a Joseph in 1871 missing from 1881 census.
The 1901 census gives his dob as 15 June 1866. and the 1911 one as June 1867.
In fact, if you look at Onésime's marriage record, cited present is Louis Girard, brother of the groom.