Tattooing - how old must you be?
In America it is not against federal law to be tattooed before you're 18 but state law differs. Most states define a person who is 18 as legally an adult. However, with parental consent some states allow minors (people aged 17 or younger) to be tattooed.
The youngest people with tattoos
It's not very well known but identical multiple birth babies are sometimes given very tiny tattoos. These mean that if everyone gets completely confused about who is who, there's always a way to find out.