DS wouldn't touch the toilet. He showed signs of readiness at around 18 months, by making it very obvious at night when he needed to pee. So I'd put him on the Baby Bjorn potty that I put next to the bed, he'd pee at night, and sleep the rest of the night, which was LOVELY.
Once he was dry at night (with my help in waking up when he'd do the pee-squirm), we slowly started during the day. I had the Baby Bjorn Little Potty, 2 of them. One in the bedroom, one in the living room because he REFUSED to go in the bathroom off the living room, and there was no way I was taking him upstairs to the big bathroom every time he needed to pee.
My friends thought I was nuts!
But it worked. Did the final wash and dry of the cloth dipes a year later.
And later, when he got taller and more interested in what DH was doing, he started peeing standing up, and he does that just fine.
With the BBLP you do have to hold his bits down, to make sure it wasn't going to hit the ceiling. Though that might be specific to your own kid and what his bits do when he has to pee, LOL. If we have another child and it's a boy, I might get the non "little potty" and get the bigger one, because it has more of a guard in the front.
Anyway, just follow his lead, don't judge things based on what other kids do at what ages...he'll do what he does when he's ready! Just have things available to him when he's ready!