The age which you are first considered a human being at. Any age below 18 is highly discriminated against almost everywhere in the world and you are not yet human in the eyes of almost everyone. People under the age of 18 are legally allowed to be, with the exception of being murdered or tortured, treated exactly like slaves of the 1800's by slave owners, called "adults, parents, or gardians" for obvious reasons.
Eddy: I know I have AIDS and I'm going to die tomorrow but, I'm 60 years old and I lived 60 great years so I couldn't be happier.
Bobby: No, you lived 42 great years, the years before that you were not a human being, remember?
Eddy: Oh yea, maybe by the time you're my age, age discrimination will be illegal and people under the age of 18 will be treated the same as people over it.
Bobby: Wonder what they'll find to discriminate against after that happens, they already used blacks and gays.