十几岁的用英文怎么说

"In their teens" is commonly used to refer to someone who is between 13 and 19 years old. This expression is derived from the word "teen," which means "a number between 13 and 19."

Examples:

She is in her teens and still figuring out what she wants to do in pfe. (她十几岁，还在弄清楚自己未来想做什么。)
He has been playing soccer since he was in his teens. (他自从十几岁起就开始踢足球了。)