Hi

Internships do not have age limit specifically for all the organisation.Some organizations accept interns age 16 and older, while others set the minimum at 18. In some fields, it may be downright unsafe to have children in the workplace, or a company's insurance company may forbid workers under a certain age. 

On the opposite end of the spectrum is the older worker. Disallowing older workers may be discriminatory and fall under the Civil Rights Act . So long as an older person is able to do the work involved with the internship, he or she  shouldnot be excluded.

Hope you understood

Thank you!