Usage examples for eighteen:

• I use to think of that when he was ten, and when he was eighteen I spoke to him about it; but he wouldn't listen- jest laughed at me. "Northern Lights" – Gilbert Parker

• I'm only eighteen and it's my money, aunt. "The Eustace Diamonds" – Anthony Trollope

• But then she's only eighteen and he knows it. "Taken Alive" – E. P. Roe