There are not many age restrictions for applying for a patent. Minors can apply for a patent as long as their inventions and creations meet the conditions for patent application.
Your second question: Multiple people can apply for a patent together. If a non-service invention-creation is completed jointly by two or more inventors or designers, the person who completed the invention-creation is called the co-inventor or co-designer. The right to apply for patents and the patent rights obtained for inventions and creations owned by *** are jointly owned by all ***.