Lyric discussion by Stadge 

Cover art for Tin Soldiers lyrics by Stiff Little Fingers

No, it is "If at the age of 17 you fall in line too soon", as it refers to the military "falling in" for parades and the like. As for the song, it means a lot to me as its exactly what happened to my brother when he signed up, he didn't realise that his contract only started properly when he was 19.