At 18 months old, my younger son became interested in the potty (seeing big brother use it was a big factor, I'm sure). For about a week. Then he refused to go for a while. Then he showed some more moderate interest. But for the past month or so (he's now 27 months old), he's taken to pulling off his diapers (wet or dry) sometimes. So, I was having to clean up pee from the floor anyway, so am trying to potty-train him. I'm getting a bit of success -- he does actually go whenever I put him on the potty -- but he doesn't *tell* me he has to go. I'm trying to do better about recognizing his "gotta go" signs (the other day, I recognized he was kinda acting like he didn't know which way to go, and then grabbed himself), so I was able to get him to a potty in time. But mostly, it's just me telling him to go.
My older son was a lot easier to p-t, because I accidentally left him diaperless one time, and when he knew he had to go pee-pee (and we were *not* working on p-t), he said in a distressed tone, "Oh, mommy, I go pee-pee!" so I took him potty, and he went. My younger son couldn't care less if he goes pee-pee *anywhere*! My older son also drank a lot more liquid, so it was easier for me to keep track of his drink-pee cycle. My younger son sometimes won't drink at all (even when given a choice between milk or water, he sometimes chooses nothing), so if I were to take him as often as every 15-30 minutes, many times he has nothing. And then gets frustrated that I've put him on the potty and interrupted his play. But lately, when I've asked him if he needs to go potty, he will either truthfully say no or get up and run to the potty. So we're getting there.
Honestly, I don't think my son is quite ready, but his pulling off his diaper leaves me no choice. Just as different kids learn to roll over, crawl, walk, and talk at different ages, so some kids p-t at different ages.
I'd keep going with your son, though, because I think in his case "practice makes perfect." As long as he's not frustrated by being put on the potty, and you're not getting frustrated by putting him on the potty, then I think this encouragement to use the potty -- to get him accustomed to going in the big white bowl instead of his diaper -- is a good thing.