I once got involved in an argument with my youngest sister about when her daughter should be "told" who her father was (they were still married, when this conversation took place). Her daughter was two when the split happened, so may well have had some recollection of him anyway.
There had been some domestic violence (my sister nagging the man like hell I suspect, and he probably had a bit of a history of some violence against a previous partner/wife we learned later). So my sister was opposing telling her daughter at the time I was urging her to do so, still resenting what he had done, and my niece was probably at a similar age to the child we are discussing here.
The upshot of it all was completely unexpected to me, my niece got to discover who her dad was, though not by her mum having to tell her, but because my sister got back together with her dad for a short time. I never understood how she could do that, given what had happened, but it did solve the other problem.
Since then the father has chosen not to take part in his daughter's life again. However, my niece talks about him occassionally - he is a great big man, who works very hard, and is jovial most of the time. I think my niece is proud of who her father is, so seems to be progressing very well in her life (she may become a star one day, having a wonderful singing voice, that is making her already in demand for local concerts etc.). One day she may seek her father out again and I guess they will overcome their estrangement better than some of us might be able to do so.
I hope my story is of some use to you, and that you come to make the right decision, whatever that might be.
All the best, Graham