Hello everyone, I have a question: when did your little one start talk…

Hello everyone, I have a question: when did your little one start talking? Mine doesn't say anything in particular, just repeats "dad" and doesn't want to repeat anything else, he loves books and flashcards, he constantly asks to be read to but never repeats, tried many different ways but can't get a word out even animal sounds aren't imitated, although he understands everything we say, is it worth thinking about at 1.5 years old or is it still early?