travellingthrough: You didn't specify--which are you?
Also, for those who answer, where are you from? I'm American and I believe "younger than me" is highly colloquial here. I suspect there may be some differences if you are from England or another part of the English-speaking world.
To Kate H: I would argue that "ain't" and "don't got no" are dialectal usages which are clearly nonstandard in spoken English, while "younger than me" is standard in spoken English (at least, that is, in spoken American English).
Kate H: thanks for your add'l thoughts. I think this may be a gray area. In Michael Swan's Practical English Usage: "In informal English, we often use the object pronouns (me, him, her, us, them) after than. In a more formal style, subject pronouns (I, he, etc) are considered more "correct". [quotations are his] She's older than me. (informal) She's older than I (am). (formal) When the pronoun is used with a verb, only subject pronouns are possible." In A Student's Introduction to English Grammar by Huddleston and Pullum: "The nominative [I] is strongly formal in style, and the accusative [me] is much more common in ordinary conversation.... The more authoritarian and conservative manuals claim that only a nominative is grammatically correct.... But that is to confuse correctness with formality...the accusative variants are unquestionably grammatical in standard English." Still, I suppose I must admit that it's better to err on the side of "correctness." :)
thanks to all for your perspectives! Lexico, I also enjoyed your comments.