Hi Sarah
As Rick mentioned there will not be any details of Hitchin in St Albans library

I would be surprised if the one in the index is your William as there is no middle name or initial (although obviously not totally impossible!) I would think that it's more likely that his age is incorrect on his marriage cert.
Do you have him on any census? It might be worthwhile seeing if anyone can find any likely suspects in 1891 in St Albans. The library does have the census but it is not indexed so I would need a reference or address. Does it have his address on the marriage certificate or does it just say St Albans?
There are also a number of historical directories for St Albans in the library which may have him, but it would be difficult to be sure it's him without an address. I can certainly have a look though. If we do find a likely suspect who has been born in St Albans, I would be able to check the christening records which would name his parents - although obviously it would depend on him being christened!
Sorry I can't be more help yet.
Julie