Whenever I see late bloomers, I feel the need to mention the story of my uncle.
Aged 2, my uncle fell out of the window of a two story house. He survived, but spent years in and out of hospital, and my grandmother was informed not to 'expect much' and under any circumstance she must not attempt to 'teach' him - letters, numbers etc. He went through elementary school 'behind', failed important examinations and was put in the 'slow' stream.
Today, of Grandma's four children, he is the one with the Phd., the author of numerous successful books, accomplished musician, linguist and all round academic.
We'll never know if the accident is what led to delayed achievement of if he would have been a late bloomer anyway, but the story always gives me pause.