What age range were in World War 1?

in the first world war boys as young as 13 were in the war, they were very nation proud and wanted to make their country proud so they lie about their age and if they weren't convincing the Sargent will ask them to go round the corner and come back and say that they were the age of 19. So many lad as young as 13 died to make their country proud and to keep harm away form their love one so they won't have to suffer