I have written to him for a long time.
Is it possible to write that? Someone told me that this sentence was not valid, but I don't understand why? Is it true?
It means for me that I still write to my friend or that I have recently stopped.
I want to say that I have very recently stopped writing after sending many letters during a long time, say six years. Is the sentence below okay?
I have written to him for six years.
but I recently stopped.
What difference, if any, does for a long time and for six years make?
If present perfect is not possible here, what tense should I use?