Aasimar are addressed in Blood of Angels. "Women that carry an aasimar child report easy pregnancies and deliveries..." There's an entire page of info on Childhood, another on Adolescence, etc. They don't come out and say it explicitly but there's no sign of any time disparity; they are described as maturing to age 5-6 like other human kids and having some issues during puberty with their peer group. BoA says, "An aasimar might spend a good portion of her childhood thinking of herself as human." This is odd as the Advanced Race Guide indicates that the adult age of an aasimar is 60, which would seem to indicate there's some kind of slowdown between birth and there... Same situation for oreads etc.

Bastards of Golarion has nothing to say about this for the other races, it's more of a crunch book really.

I think this falls into the general category of "poorly thought out things in the D&D cosmology," which are manifold. Just like the high intelligence of many aberrations, it's an interesting note trotted out every once in a while as a plot point and then conveniently forgotten 99% of the time.

So your playbook:

• Decide if you care - it's a magical world and these are magical crossbreeds, there doesn't have to be one answer and you can be as inconsistent as you want
• Decide if you just want to say "they mature at the same rate as anyone else" and ignore the adult age listed in the books
• Decide if you want to let players decide based on their own concept of their PC's background

First up, the RAW. This is pretty simple: Divine Sense works on celestials, fiends, and undead. Player characters are all humanoids (see page 11 of the PHB), and the Tiefling traits do not say anything about making the character a fiend in any way.

Next, we have the lore. In 3.5e, tieflings were the descendants of actual fiends, whereas in 5e, they are simply a race that has had the essence of Asmodeus infused into their bloodline. So they're a bit less fiendish than they used to be. If we look at the fiend type in the Monster Manual, it says that

Fiends are creatures of wickedness native to the Lower Planes.

Tieflings definitely don't fall under this category lore-wise, because they are a humanoid race native to the Material Plane.

Trying to argue that abilities that work on fiends should work on tieflings is like trying to argue that abilities that work on dragons should work on dragonborn, but what you have to remember is that fiends are the physical embodiment of evil. The differences between tieflings and real fiends are insurmountably greater than the differences between dragonborn and dragons.

The taint in the tiefling bloodline is a devilish one, so if they were fiends, they would be devils. Taking a look at the description of devils in the Monster Manual, we see that

Devils personify tyranny,

and that

Devils live to conquer, enslave, and oppress.

The fact that tieflings are allowed to be any alignment contradicts this, and similarly, tiefling characters are allowed to do things other than conquer, enslave and oppress - they're definitely not devils.

Finally, if another argument is needed, Jeremy Crawford agrees that tieflings are humanoids, not fiends, and can't be sensed by a Paladin's Divine Sense.