Learn Finnish: Epäilty on nuoren pojan ikäinen. - The suspect is the age of a young boy.

If the genitive modifier is just a single word, it usually forms a single compound word with the adjective (like samanikäinen, "of the same age"). However, because the modifier here is a phrase made of two words (nuoren pojan, "a young boy's"), the pieces must be written as separate words.

Why do both nuori and poika end in -n?

They are in the genitive case, which is used here to mean "of" or to show possession. In Finnish, adjectives must agree with the nouns they modify. Since nuori (young) describes poika (boy), both words get the genitive -n ending to make nuoren pojan ("a young boy's").

Why does the translation say "the age of" when ikäinen is an adjective?

The word ikäinen is an adjective created by adding the -inen suffix to the noun ikä (age). It translates literally to something like "-aged". So, the sentence is literally saying "The suspect is young-boy-aged", which we translate into natural English as "is the age of a young boy."

The word epäilty means "the suspect", but it looks like a verb form. Why?

It is originally a verb form! It is the past passive participle of the verb epäillä (to suspect), meaning "suspected". In Finnish, it is very common to use these verb forms directly as nouns. So, "the suspected (person)" simply becomes "the suspect".