@beepbeep321
I personally would pursue a diagnosis so you find out one way or another. Having a diagnosis won't hurt. He may be coping well now but things could change and the support will already be there for him. It's helped us at school - he's been to the school nursery and then to reception. He gets taken out of class a few times each week with a couple of the other children where they work on things like social skills etc. They have a lot of extra patience with him and he's allowed to help them do certain jobs every day (because he's a stickler for rules and things being done right). They've embraced him. He's coped well so far so could have possibly done without the help however he could suddenly start struggling and I feel happier knowing the help/extra patience etc will be there if/when it's needed. Year 1 is going to be very different to reception so who knows how he copes.
I'm no expert but this is our experience of it all..
It took almost 3 years to get his diagnosis. I started when he was around 15months when I realised he should have started babbling, clapping, waving or pointing and he wasn't doing any of it. He was spinning in circles, doing weird things with his eyes, tip toe walking. He has always been a good baby/toddler/kid, he would just do his own thing, wouldn't tantrum, do anything 'naughty', slept well. He wouldn't eat wet food/food with sauces. I wasn't allowed to join in with what he was doing he wanted to do it alone. Doesn't like sudden loud noises, alarms, hand dryers, it was difficult trying to potty train him because I couldn't take him to public toilets when out as the fear of the hand dryers was too much. He has never really played or used his imagination, he just tends to sort & collect sets of things, & do puzzles or games rather than play with toys, his memory is amazing so by 3 you could tell him a mr men character and he'd tell you what number the book was in the set by memory. He knew all 50 odd mr men and 30 odd little miss by memory. Schools been too easy for him so far, well maths has, whilst the kids are learning to count and order numbers to 20, he's already doing it to 100. Same with shapes, sums etc.
He blends in with other kids on the surface, nobody has a clue he has asd. He has lots of friends at school (though also likes to have time in his own). He's well behaved. It's only when you watch closely he's different. Social skills are lacking slightly, he can't read other kids very well, though I don't know if that's normal for his age or not, he's my eldest so no experience of kids his age.
Sorry that's quite the ramble. Not sure if it's helped at all!