Firstly, is your son in creche? If not, then there's really no pressure or time constraints. I would suggest bringing the potty out, have it in the bathroom (or wherever you change his nappy), tell him what it's for and ask him if he wants to sit on it. If he says yes, great, let him. If he says no that's fine too, just say that's where we wee and poo or whatever.
When I used to au-pair the little girl loved the toilet, so every time I changed her nappy I asked her if she wanted to sit on the toilet. It was great fun for her even though she never actually did anything on it. Then one day, she asked to sit on it, over and over like 20 times I had to take her nappy off, put her on the loo, put her nappy back on, repeat. After about the 20th time she said "no nappy". I told her she must tell me when she wants to wee and I waited for the wet floor. I kid you not, from that moment on she was totally toilet trained, no accidents. It's like she herself just decided now was the time and that was that. She was about 28 months at the time.
If, however, your son is in creche (like mine is), then you sometimes are pressured into encouraging potty training earlier. I haven't been told by the creche when we must start, but I'm fairly sure it will have to be this summer, as soon as the weather starts warming up.
He doesn't like having nappies put on so loves to run around the house naked. Then he wee's on the floor and tells me "mess" and shows me where he wee'd. In a sense I think it's good because it lets him know what's happening and he can literally see what the sensations he feels result in. (in another sense I worry he's learning it's ok to wee on the floor).
we've had a potty (actually 2) in the bathroom for about the last 6 months and he point blank refuses to sit on them. He also refuses the toilet. So I don't push it. I tell him when I'm going to the loo (he's now started saying "daddy wee wee" whenever my husband walks into the bathroom), so he knows what you're supposed to do in there. And I'm just hoping one day soon he'll decided he wants to wee on the toilet or potty. For now, when he starts wee'ing on the floor (which he often manages to stop as soon as the first squirt is out), I put a terry square (spoegdoek) on the floor in front of him and tell him to wee on that rather. For some reason he's quite happy to do that and so he crouches down and wee's on it. So I figure in a sense I'm teaching him how to kind of control his wee - wee on command in a sense.
Really hoping at some point he'll choose the potty/toilet rather than the cloth but I'm not putting any pressure on him yet.
Not sure if any of that helps at all.
And really, unless there's a time contraint imposed by a daycare of sorts, it's entirely normal for kids to only start showing an interest in potty training around 2.5 years, some even closer to 3.