Guillow's balsa model airplanes are generally recommended for ages 8 and up, preferably with adult supervision. This also depends on whether you are constructing the plane from a kit, in which 8 and up is recommended, or buying a constructed plane, in which 36 months and above is safe.
The foam and balsa wood materials that make up the airplane kits are thin and breakable. Children would have a hard time constructing them because of the delicate parts. There are some small parts as well. However, the kits are simple and can be constructed in minutes with adult supervision. Constructing the planes is for ages 8 and up, but after that, younger children can handle them without difficulty.
Planes that are already constructed come with stickers for decoration. Normally, placing the stickers is all the work required before they are ready for playtime. The propellers are rubber powered and pose no threat in cutting or hurting. 36 months and above is recommended for constructed planes.