Sorry to continue with questions, but you seem to know quite a lot about these two -
what is the source of this info?
FreeBMD is a free resource of the index to marriages, from the General Record Offices indexes.
I cant remeber the exact website address, but you can easily find it via google, or better stil via the links on the beginers board on here.
You wont get and exact date of birth from that, you will need to purchase the birth certificates for that, but you will narrow it down to the quarter in which the birth was registered.
Hopefully you will see the marriage there too, but that will be a lot easier to spot if you know approx when it took place, hence my questions about the censuses!
So, you have a 14 yr old John Hornby in 1881. But in order to be sure that this person at some time marries a Mary Jan Bainbridge, you must have some more info, or else it is a very big straw you are clutching! Did John and MAry have children? Is that where you are coming from? If so who are they - perhaps we can find them on a later census with John and Mary? But then that wouldnt give you John's father .... would need marriage cert for that, which then may or may not lead to this 1881 entry.