This is the 7968th most frequent Polish word.
młodych
"Young" (plural or genitive form).
Here, 'młodych' is used as an adjective in possessive genitive, describing 'ludzi' (people), and it agrees in number and case with the noun.
Spotykam wielu młodych ludzi w parku.
I meet many young people in the park.
In this example, 'młodych' functions as a substantive (acting as a noun) and refers generally to young people.
Dla młodych świat jest pełen możliwości.
For the young, the world is full of possibilities.
Here, 'młodych' is in the genitive case, showing possession or relation to 'zachowanie' (behavior), referring specifically to 'the young people.'