There is only one exception for purchasers below the age of 18 years to legally buy razor blades, and that is if they are permanently enclosed in a cartridge or housing where less than 2 millimetres of any blade is exposed. These would include disposable razors and replacement razor cartridge heads.
A knife (plural knives; from Old Norse knifr 'knife, dirk') is a tool or weapon with a cutting edge or blade, usually attached to a handle or hilt. Most modern knives have either fixed or folding blades; blade patterns and styles vary by maker and country of origin. Knives can serve various purposes.