@Usingthings I honestly would ignore any comments from anyone who "just did whatever at age 2" and it was all fine. Some children do just find it harder than others, and I think it is very hard for someone who had a fairly standard potty training experience to imagine what it's like to have a different experience. People said to me "you just need to sit him on the potty" which is easier said than done when you have a very distressed child going rigid! I think the majority of children are physically ready at age 3, but emotionally some aren't. I don't really think there are any cues you can necessarily look for to see if he's emotionally ready, just trial and error.
We first tried my DS at around 3 and it was awful. He refused to wee on the toilet or potty, but was so distressed about accidents. We stuck at it for a long weekend but he was so miserable and I felt so stressed out we gave up. We tried again mid November (at 3 years 5 months) and he seemed much less stressed by the whole thing, so although we still didn't get a single wee in the potty for 4 days I stuck at it. Day 4 we got our first wee, so we stuck at it a bit longer. One week in we were getting very few accidents, but I would still have to keep taking him when he looked uncomfy rather than him initiating it. I think it's really only been over this Christmas break (about 5 weeks in) he has been confidently telling me he needs a wee. Also only just starting to poo in the potty, although usually does it in his nappy first thing before we get his pants on. And he's a few months older than your son!
It's hard not to take it personally and feel a bit crap, but my daughter successfully potty trained a whole year earlier at 2 1/2 so I don't think it was anything major I did. And I'm sure the same applies to you - we are all only doing our best!
I think one thing that can take practice for them is going from learning to hold the wee in most of the time to then fully emptying the bladder on the potty. Which is why sometimes they'll have a wee then an accident a few minutes later, but this will come with practice.
Personally I think if he isn't getting distressed if you stick at it he will get there over the next few weeks but it might just take a bit longer than some children. However, if you are feeling really stressed then I think it's worth taking a break - my son's nursery said they have a few every year that take to 3 1/2 so there's no harm in trying again in a few months if you need to for your own mental wellbeing! Especially as you have ages until school (my son is starting next September which massively added to my stress!).
Good luck - it is so stressful, but one day it will click and this will all be a distant memory.