You may well find that John Thomas Forster had no known father.
With his exact birthday, 19.2.1891, there are only two possible children registered, one in Medway, Kent and the other in Gateshead. He is probably the Gateshead one, in which case there is no mother's maiden name given, i.e. his mother was not married.
Looking at the 1891 census for Gateshead (taken on 5th April) there is a John Thos Forster, 6 weeks old, living as grandson to John Forster, 62, widower, coalminer. This John has two unmarried daughters with him, Margaret 27 and Elizabeth 21 so either could be his mother.
It is worth bearing this in mind when you get the marriage certificate as people often put the name of a step father or just made up a name if they didn't know a father's name.
If the above John Thomas Forster is correct you will not find him in 1901 or 1911.
His mother was Elizabeth Forster, she married John Charlton at Gateshead Q1 1894.
In 1901 the family are living in the house where the Forsters had been in 1891, Dog Leap at Ryton Woodside. with them are Elizabeth's unmarried sister and brother. John Thomas is now called John Thomas Charlton.
RD Gateshead, sub RD Winlaton
In 1911 the Charlton family are living at Addison Colliery Blaydon and John Thomas Charlton is an "engine cleaner, railway" He is 20 and his parents say married 18yr but he is given as son to John Charlton so maybe he was his real father?