Because fewer folk observed birthdays and maintained an awareness of such matters the way we do today, there was a tendency among many to understate age in official records, in contrast, the introduction of the Old Age Pension in 1908 to the over 70s caused a noticable phenomenon of age 'inflation' between the 1901 and 1911 Ireland censuses. In this case, I would hazard that the net effect brings William and Martha closer to the truth in 1911. In relation to speed of finding, a website that I subscribe to has transcripts for various Irish church records, while useful in itself, it also acts as a convenient 'index' for searching the NLI church record images, for I always prefer to see the originals if possible.