Many modern American tattooist will tell you, "When you should get a tattoo, the tattoo god will tell you that it is time." Check out this article on Hawaiian arm tattoos on the site. In the 1970's, American tattooing discovered primitive, tribal tattoos. People wanted simple designs with meaning and they began copying designs, primarily from the islands of the South Pacific.
Another approach is to visit tattoo studios in your area and look at the designs and photo displays on the wall or their album to search for inspiration, but keep in mind, don't limit your imagination to what someone else already has, be creative.
A belief goes that if a girl can't take the pain of tattooing, she is un-marriageable, because she will never be able to deal with the pain of child birth. If a boy can't deal with the pain he is considered to be a bad risk as a warrior, and could become isolated from the tribe.