My understanding is that the difference is more geographical and than generational.
Substitution of adjectives for adverbs has been a feature of American English for a long, long time. This is not a 'youth' thing. In fact, unless I'm very much mistaken, AE speakers of all generations could say "You did real good". I'd imagine that it's not impossible that a well-educated young person who's learnt how to 'talk proper' (sic) might even be embarrassed to hear their less educated parents or grandparents speak in this way.
This is not generally a feature of British English. If an English person were to say "You did real good", we'd wonder why they were trying to speak like an American.