I often hear these mistakes made by German speakers who are learning English.
They say: I know him for ages.
The tense is wrong in this sentence.
Remember if we are talking about someone we still know now we need to use the present perfect tense here (have/has + 3rd form of the verb) because this is something that started in the past, is still true now and continues into the future. It is ongoing and unfinished.
Correction: I have known him for ages.
Have fun learning English!
Louise