This is a corrido-style love story with a big age gap in the middle of it. The singer locks eyes with a woman and feels the spark right away: "Las miradas se flecharon" (our looks struck each other like Cupid's arrows). Flechar comes from flecha, an arrow, so in Spanish you literally get "arrowed" when you fall for someone. The problem? "Por su edad, pos tiene 20" (because of her age, well, she's 20), and he is a lot older.
She brushes it off with the line that gives the song its title: "Dame una oportunidad, que ya soy mayor de edad" (give me a chance, I'm already of legal age). He worries about "qué diría la sociedad" (what society would say), but she has made up her mind. She doesn't want "un Ricky Martin" (a Ricky Martin, meaning a pretty pop-star type) or a guy her own age, because supposedly they haven't learned how to treat her. Look out for "le vale la sociedad" (she doesn't care about society): valer here is Mexican slang for "not giving a damn". And his answer is pretty cheeky: "A mí tampoco, ¿para qué me hago del rogar?" (me neither, why play hard to get?).