If you are looking at aircraft, I would start with 1/48th scale rather than 1/72nd.
The simple reason is the parts are larger and easier to place. They are large enough to be fun, and not too large.
For younger hands, I think 1/32 may be too large. Plus the 1/32 kits tend to have more parts added.
The stalwart brands for many years for young modelers were Revell and Monogram. The two companies are actually now owned by
the same holding company now.
If you shop online, such as Amazon, you can shop for Revell or Monogram or Revell Monogram. All of them will bring results.
You can also go to the website https://www.revell.com/index.php
Tamiya is also out there, from Japan. I would hold off on these kits for awhile as they tend to be more detailed.
You will want a variety of paints and brushes for adding details. Eventually he might want to work up to a simple air brush, but this
will take some patience. Keep in mind that military colors are "flat" as opposed to glossy. At some stores you can find
a starter pack with with a dozen or so military shades.