19 month olds really have a mind of their own. My little guy is 33" and he fits my neighbor's Trek (?) trike easily & so does my 5 year old. The higher quality ones last a long time. Now, the thing is, of he can steer by himself, don't expect to safely or quickly go anywhere. If you're looking for slow sidewalk exploration (includes you carrying bike & him at points) or driveway/playroom play, then a trike or balance bike would be best.
These are BALANCE BIKES
& they're AWESOME for teaching toddlers and preschoolers the basics of balance before they're big enough for a bike without training wheels. I LOVE them! Best bike thing for young children in my mind!
Now, if you want something that you can go for a little walk down the street with, I'd do a trike with a belt & a handle for YOU to push. Like these TRIKES WITH PUSHBARS
The pushbars come off when the kid wants to ride by themselves. My 3 1/2 year old still fits the Kettler beautifully, but the cheaper models were long outgrown by her.
By all means, PLEASE support your LBS, they're great & the customer service is unbeatable. If they don't have anything I'm talking about then, I've bought from that company I linked you to before & have some coupons from them if you decide to order from them:
TENOFF49 - Saves you $10 off first purchase of $49+ and gets you free 2nd day shipping
and you can combine it with:
PLUS10PCT - Saves 10% off first purchase
I do find with tall kids, you almost HAVE to buy the higher quality stuff, because the cheaper cycles are made for the regular or tiny sized kids. The higher quality items seem to be designed to last for older ages (which isn't actually older for your tall boy!)... Now, next year good luck finding a potty chair that he doesn't dwarf.
So, my bottom line is, I'd probably buy balance bike & know that he'll play with it now but grow into it for many years. But, if I want something to on walks with, I'd buy a trike with a pushbar.