This is the 136th most frequent Hungarian word.
fiatal
"Fiatal" means "young" in English.
Here, 'fiatal' as an adjective describes the noun 'ember', meaning 'man', to indicate that he is young.
A fiatal ember a parkban sétált.
The young man was walking in the park.
In this sentence, 'fiatal' is used as an adjective describing the noun 'koromban', which means 'in my age.'
Azon gondolkodom, milyen fiatal koromban voltam.
I am thinking about how young I was in my youth.
Here, 'fiatal' functions as a nominalized adjective, representing 'young people' as a plural generic term.