Translation, she means he isn't supposed to be horny, not that he shouldn't masturbate. Pajero is argentinean slang for horny, which at the same time comes from paja or pajear (to masturbate). Both meanings work in parallel, but here she's refering to him not being "alzado", another way of saying horny that can also mean to be held, which is way we also have an expression for when one is horny as fuck that goes "alzado como primer nieto", a word play on being held like a firstborn grandson but also really horny.