Also, does your teen have corrected vision? A 12" display would be less than ideal if so. The MBA display is larger even if it is lower resolution. Also, while color saturation is far from ideal, the screen is very bright.
That statement doesn't make much sense. The more statements like these you make, the more convinced I am you have very little experience with the 12" MacBook.
The native resolution of the MacBook is 2304/1440, which is run as if it were 1152x720. At that resolution, the pixel density is 226/
113 ppi. However, with the 2017 model, they actually default it to 1280x800, and that resolution, the pixel density effectively is
126 ppi. And because it's a Retina screen, text remains uber crisp at that resolution even though it's non-native. There is also the option of 1440x900, which gives a pixel density of
141.5 ppi.
In contrast, the 13" MacBook Air has a 1440x900 screen, with a pixel density of
128 ppi. In terms of OS elements and font sizing, the smaller number is better. So, the native resolution of the 12" MacBook would be the best and by far much better than the MacBook Air in this regard. However, Apple no longer defaults to the native resolution. Their default is now 126 ppi, which is basically the same as the MacBook Air's 128 ppi, but with the slight advantage for sizing going to the 12" MacBook. However, the MacBook is still better overall for text quality.
For those with eagle eyes, they can choose the MacBook's 1440x900 resolution, but I don't recommend this for most people. But at least it's an option, and it still looks good.
On the MacBook Air, the only feasible resolution is the native 1440x900 resolution. Anything else and it will look like crap. If you have bad eyes, for a 13" screen a 1280x800 resolution is actually better at 113 ppi, but on the MacBook Air it looks absolutely horrible.
Now, if you want a 13" screen, then the only option here for someone with not-so-great eyes is to get the Retina MacBook Pro. Native resolution on that is 2560x1600 / 1280x800, and it looks awesome.