This is the 12420th most frequent Polish word.
młodszego
"Of the younger" or "younger."
In this sentence, 'młodszego' is used as an adjective to describe 'syna' (son), indicating that he is younger.
Mój brat ma młodszego syna.
My brother has a younger son.
Here, 'młodszego' is combined with 'brata' (brother), and modifies it to specify that the brother is the younger one.
Nie widziałem młodszego brata od tygodnia.
I haven't seen my younger brother for a week.
In this sentence, 'młodszego' is employed to describe 'siebie' (self), characterizing the 'self' as a younger version.