I have done an internship. BUT NOT AN INTERNSHIP LIKE THAT!
It seems to me that you have been offered something lucrative! It is a blessing. I hope that you take it. It says alot that you are so young and they want to reward you because of your performance. I wish you well in your endeavors.
I think the most you or ANYONE can gain from taking an internship is EXPERIENCE and NETWORKING with colleagues in your area of work.