Learn Finnish: Tiedätkö, minkä ikäinen epäilty on? - Do you know what age the suspect is?

This is part of the core pattern for adjectives ending in -näköinen, -kokoinen, or -ikäinen. They require the describing word that comes before them to be in the genitive case. Here, the question word mikä (what) becomes minkä to form minkä ikäinen (literally "of what age").

Why is minkä ikäinen written as two separate words, while words like samanikäinen are written as one?

As a general rule, when a pronoun (like mikä, tämä, or tuo) acts as the genitive modifier, the phrase is written as two separate words (e.g., minkä ikäinen, tämän kokoinen). When the modifier is a standard adjective (like sama), they are typically written together as a single compound word (e.g., samanikäinen).

Where does the noun epäilty (the suspect) come from?

It is a noun created directly from a verb! It comes from epäillä (to suspect). Specifically, it's the passive past participle form, which translates to "suspected" or "has been suspected". In Finnish, it's very common to use these participle forms directly as nouns, so epäilty literally means "the suspected one".

Why is the word order epäilty on instead of on epäilty?