He isn't' too young to be potty training. We as a society have just decided to leave it till they are older because it's supposedly easier....
In any case, sounds to me like this is a control issue between you and him, if he goes at school. With my daughter, I just make using the potty an expectation, like brushing her teeth. So, she knows the rules: we go when we get up, we go before we eat, we go before we leave the house. The thing is, you don't ask. You tell him, and then offer options: which potty are you going to use, mommy's or yours? Are you going to take down your pants, or am I? Do you want to collect your toy bag now or after you go potty? If he shows resistance, you ignore it, and then just say, "Ok, I'm going to count to ten and if you haven't decided, then I'm going to decide for you."
Resistance doesn't mean he isn't ready, it means he is being at toddler.
Also, get rid of the pull-ups. Buy some Gerber trainers that hold a bit of the pee, do a big celebration of his successes over the past two months, and tell him he is graduating to being a big boy. Tell him that once he starts putting all his pee and poop in the potty, then he can pick out his undies himself (my daughter wouldn't poop on the potty for me, but elmo underwear motivated her). Find something to motivate him, and then don't turn back. You will have to take him to the potty at the beginning. It won't take you long to figure out the timing, and if he is going at the daycare already, you could ask them how often they take them --they will have a set schedule and it won't be optional!