H.B.
I know you are looking for a trike, but you should look into getting him a Fropper.
My 25 month old son has been getting use out of it for a while now. We also have a used Kettler with push bar (got second hand for $12!) and he doesn't have much interest in it yet. His feet touch the pedals and he "pedals" when I push him but he's just not ready to take off on it yet.
The Fropper has 4 wheels and has a sort of bounce in the seat. He'll walk that thing all the way down the street to the playground! It's also ok to have indoors if you have the space. You can get a parent push bar for it but I haven't bothered to.
All in all, have fun and don't try to push him to use it if he's not ready yet!!!