20 months isn't too late for EC. What you may need to do, though, is do the easiest part first - night-continence.
If you can sleep with DS in his bed at night for a while and be aware of his wrigglings, you will catch more wees than if you try to go for day continence.
While we sleep we release a hormone that inhibits urine production, so it's in lighter sleep that children rouse and wet themselves. If you can catch that moment to offer a potty, you'll find more successes that build up and give you both more confidence.
For us: long weekend in Bendigo, not one nappy used, and only two floor incidents at the motel (both times, right near the potty, doh!) - all weekend we spent the days by the fire brigade running track with no nappy on, and DD held on till I could take her to the toilet, where she'd do a big long wee I'm sure there were disapproving looks because she was wearing dresses and when they lifted up she was nekked, but I knew that as soon as I put a pair of training pants on, I'd slacken off and she'd end up doing a wee...so I left everything off, and she remained dry. Not a single smelly nappy to bring home, yay!
She's waking up in the morning and able to get down off the bed (when I say 'potty'), open the door of the caravan, let herself down (prompted by 'safe safe', so that she goes down backwards) and go over to her potty for her morning wee and poo. It's starting to pay off, all this intensive cue-catching - so when people say "oh, that's so easy that you dont' have to use nappies", I tell them that it's been an intensive 17 months!