Once a person feels the need to avoid a certain event which contains mature content and the likes, such as pornographic and erotics, they have the option to use this excuse. But basically it can be used for anything which the person is too young for, even if they are not young in age.
Person 1: Hey man, wanna watch that erotic movie later at my house?
Person 2: Nah man, I'm too young for that shit. Sorry.
a transgender person who started transitioning as a teen, before the age of 20, which sometimes gives them immense advantages for passing. the opposite of "oldshit". both are common terms on the /lgbt/ board of 4chan
those fucking youngshits are lucky they could get HRT so early, meanwhile I'm a fucking oldshit hon coping (and seething) with hair loss and stuck in eternal boymode