It can take a few years for seedlings too bloom and some may be very reluctant to bloom so that aspect may not be too unusual... luck of the draw with seedlings.

If it is several years old and 5 feet tall I'm a little surprised that it doesn't go dormant esp. with 40 degree temps. Depending on what the blooms end up looking like, that could be a desirable cultivar. Does it drop some of its leaves, or does it keep most all of them?

It loses single leaves as the plant grows but it never 'molts' drops many leaves at one time. It really does not change it's habits from spring to winter. The seeds were bought on Ebay from barry-ng and were from a pendulous pink parent.
Just so you know I have two of these plants (same seed lot) both in the 5 ft range and with several leafy points/tips (don't know what you call the tips).

Could it be a Singapore variety? They don't always go
dormant.

Are the leaf tips kind of rounded or kind of pointy?

Rounded leaves are usually Singapores.

There is a difference between the leave on the bloomer and the non bloomer.

Here's the crazy thing about plumeria: they have a huge number of genes--more than humans, I'm told--so the potential number of different combinations you can get from seedlings is also huge.

Just like human children, plumeria seedlings can either strongly resemble their parents and siblings, or can be completely different from them. Your seedling siblings are displaying just that.

I wouldn't worry about the not-dormant one. The blooming will happen when it's ready, which could still be a few more years. They usually take between two and six years under good growing conditions to reach blooming age, but have been known to occasionally take much longer, especially if their growing seasons are shorter than what they'd get in the tropics.

That non-bloomer sure looks like a Singapore to me.

That rounded leaf is a dead giveaway.

That first bloom can take quite a while.

I'd say that, overall, you're nothing to worry about.