He has always been interested in books and reading/writing. He could write his own name from 2.5 and can write anything you want as long as you spell it to him, even back then. He is 3.5 now.
But recently it seems to have excelled. He has started picking up books for the first time and literally reading them (my Mum will bring at least 3 new books a week, our house is packed full!) At soft play he picked up a packet of Quavers and it said 'Time for an adventure' on the top. He read it out loud. So I tested it - give him almost anything and he can read it. Or at least sound it out ie for entice he will say rice or nice. I have never taught him this, I read him a couple of bedtime stories every night before bed and that's as far as my input has gone.
He can do simple maths like adding and subtracting numbers under 10 (8 minus 2 or 5 + 3)
On the tube today he read out every stop on the Piccadilly line and what zone it was in. The only stop he could not get on the whole line was Caledonian Road. 
I am now thinking I have to act on this. He is ahead of most of his friends who went up to school this year. I am really worried that he will start school in September and will be taught things like this that he already knows. What do they do with children who can already do it when they get to school 
I just don't know how to go forward for the best, other than to keep encouraging him, he love's it. Should I see a health visitor?