Generally speaking, the kids who develop later tend to be better as adults. They get more of the pre-pubescent growth and development before puberty kicks in. In my area, the very early developers I can think of are a 16yo 400/800 (1), formerly top 15yo 100/200 runner (2), national best 100/200 runner for 16yos (3). (1) has improved 1.5 seconds over 400 from 13-16, (2) has barely improved at all from 13-15, and (3) ran 21.7 for 200 when 13, and now at 16 can't break 22. Another holds the National 15yo record (U16) for 100 and 200, and now at 18 can barely run those times.
Those are age spans (13-16) when normal developing boys improve massively. Those kids had that massive improvement at 10-13.
As I say though, who knows. If he's already at 1.50 level, then even if he's like a 17yo in terms of development, normal 17yos still improve a few seconds over 800. And he only needs to improve a few seconds to make it to the Olympics.
As you say speeder, he's certainly got a better chance of making it than someone who wasn't very good when younger.