Learn Finnish: Nuoruudesta pitäen raittius on ollut selkeä valinta. - Since youth, sobriety has been a clear choice.

The postposition pitäen (meaning 'since' or 'from') strictly requires the word it follows to be in the elative case (-sta/-stä). It marks a starting point in time, so nuoruudesta pitäen literally translates to 'starting from youth'.

Could I use lähtien instead of pitäen in this sentence?

Yes, you could absolutely say nuoruudesta lähtien. When establishing a starting point in time, pitäen and lähtien are essentially interchangeable, and both require the elative case. However, pitäen can sometimes sound slightly more formal or appear in fixed expressions like alusta pitäen (from the beginning).

How exactly does the stem of nuoruus change to form nuoruudesta?

Nuoruus is an abstract noun derived from the adjective nuori (young). Nouns ending in -uus or -yys change that ending to -uude- or -yyde- before adding case suffixes. Therefore, the base nuoruus changes to the stem nuoruude-, and we add the elative ending -sta.

Why is selkeä valinta in the nominative case instead of the partitive?