5 or so. I remember learning, but I had no idea of what age I was. I have trouble with memory in that way. Great memory, but no talent for organizing it chronologically. Then I remembered that my brother was in kindergarten that year, so I put 5 or 6. Then I remembered that they changed the start age by one year, so he ended up going twice(so he wouldnt stay home for a year), so I adjusted it to five.
I dont recall having any difficulty learning, but i dont have any memories of riding much after that, until we moved. Perhaps I didnt have a bike?