The marriage record in the IGI (8 March 1864, Lezayre) has Husband Age at Marriage: 20, Wife Age at Marriage: 21, which fits William's bapt date.

You need to see this record to confirm you have the right marriage, and to get the details of residence, fathers' names and occupations, etc. (similar to the ones I gave you from Maughold, except that you will also get witnesses' names which I don't have for Maughold). This is particularly important for Elizabeth, because Christian was such a common name that it can be difficult to identify the right family.

The parish register copies can be seen at the Manx Museum or on LDS film at Family History Centres worldwide (see in the phone book under Church of Jesus Christ of Latter-Day Saints).

William's marriage should be on this film:
Baptisms, marriages, and burials 1849-1883 Sulby, baptisms 1878-1883 FHL BRITISH Film 106181

Sue