No, nothing to do with IOM history. I meant that as he got married in NZ in 1900 there would have been no chance that this William was the right one if he had appeared in the 1901 IOM census.
The ages in censuses were not usually completely accurate, but James's and William's ones were pretty consistent. The 1891 census was held on the night of 5/6 April.
Had you heard of brother James before? I couldn't find him in the IOM or England in 1911, so he might have followed William to NZ. I have heard of people going to NZ via USA in the late 1800s/early 1900s - actually I had a Scottish relative who set off for NZ and Australia to visit his relations but stopped off in the USA and never left.
If you'd like to see some IOM history and the different parishes have a look at Manx Notebook: www.isle-of-man.com/manxnotebook/
You can "Search" for particular names or places.
For a parish map: www.iomguide.com/parishmap.php
Sue