I start talking to her in both ways (full sentence and one word at a time) She started talking at the age of 1 year (if I remember correctly) but not in full sentence just simple words like mummy daddy nanny etc. But definitely she understood what we speak because we dont use baby language, we introduce educational songs videos. Sing nursery rhymes, showing flashcards.
In my case mum it kind of late around 3. But now he is 6 he won’t stop talking, haha. :)