Translation:In those years, this tall man treated young people very badly.
- Use long and short to talk about length (horizontal distance). You can also use long and short with time, books, words/sentences, hair, and legs:
Ex:The movie is really long – about three hours.
- Use tall and short to talk about height (vertical distance) – especially with people, but sometimes also with buildings and trees.
EX: My brother is really tall. There are many tall trees in the Amazon rain forest. :))
very badly - it's an adverb
I wouldn't say it quite that way - but
In those years, this tall man behaved very badly toward young people.
would be o.k. (Probably not among the ones currently accepted though.)
A natural variation which is accepted is this:
In those years this tall man treated young people very poorly