What was life like for teenagers in England that were in World War 1 IN 1900s?

There was no such thing as a “teenager “ anywhere in the world in the time you ask about. People were children and then adults. The term “teenager “ doesn’t even enter the vocabulary until 1939 and it still took until the 1950’s that what we call a teen developed. The idea of a “teen” today also goes later in life than in previous generations.