Explosives are divided in 5 classes: 
Class 1 - Powdered explosives and similar explosives. 
Class 2 - Dynamite and similar products. 
Class 3 - Deflagrating explosives and similar explosives. 
Class 4 - Pyrotecnical artifacts(??) and products with similar explosive effect. 
Class 5 - Safety ammunitions and pyro toys. 

Classes 4 and 5 are fireworks.
They can be sold to people of age 18 or older by licensed vendors with a fireproof storage. 

Some pyro toys and very small fireworks, classified product by product by the Ministry of Interiors, are of free sale (no need of a licence) and can be sold to childrens as well. Every explosive product must be submitted to the Ministry of Interiors Commission for Firearms and Explosives, to be classified into one of the classes above, or to be excluded from those classes. There is no need to submit an actual sample of the product, but they ask for the exact formula and the specification from the manufacturer. If this is written in a foreign language, an official translation must be provided with the request of classification. The explosive classes have nothing to do with shipping classes. This means that a product shipped as 1.4S has to be classified anyway. 

Model rocket engines have been excluded from the pyro toys and firework classification and are of free sale.
They cannot be sold to people under 18, but of course their parents can buy them, and children must use them under adult supervision. 
The propellant weight limit is 113 gr. 

The flight of rockets must follow a mix of a general guideline used for model airplanes and the NAR safety code. Flight of rockets (models or real ones) is not included in any air traffic rule. 

(Source: Stefano Figoni)