The main thing in Reception is that he's happy.
I used to think that, but I've changed my mind.
My DS is in Y3 and quite a few years ahead of his peers in maths, mybabywakesupsinging. When he was in reception he was a bit like your DS in ability. He was quiet, shy, just got on with the work he was given. We thought it was far below his abilities but didn't say anything because teachers kept on about social skills and about reception just being mainly play. Things didn't improve a great deal in Y1.
By Y2 we were tearing our hair out. Our DS was miserable, used to come home crying because of how bored his maths work was, started becoming disruptive in class and exhibiting other behaviour problems.
I took it upon myself to read up a lot on the teaching of more able children, become an expert in the G&T program, and take a very hands on approach to working with the school to cater properly for him.
We've got our happy, well behaved boy back in a few months.
The only thing I kick myself on was trusting that as the school has exceptional OFSTED results, fantastic league table scores in everything etc., they can be trusted to provide properly for someone in the top 1% of ability. They can't.
Since then I've worked with other G&T coords & leading teachers, the LA's G&T rep, attended G&T meetings, conferences and seminars and assisted with G&T planning both at school and LA level. Here's my low down: Most schools are worse than DS's school. Most teachers don't know the very basics of their own G&T responsibilities and have no training or motivation to let higher ability children progress at their own speed. Quite the reverse in fact - they have motivation to "narrow the gap".
My advice: Don't leave it till Y2.