This is how internships work for those looking to get to wallstreet.
The summer after your Sophomore year you get an internship. Big bank, insurance, finance, something you can get with an econ+math major. This goes on your resume. The summer after your Junior year you use this past summer's internship and the prestige of your university to get another internship. If you perform during this internship, you will get a job offer. They will hire you back after your senior year.
Medium sized equity firms typically have 10-12 interns for summer and hire back 1/3 of them. You get report cards twice during the summer. Depending on how you rank among the interns, you get asked back. Big banks have many more interns. Standard and Poor has 150 summer interns. They ask back more of them.
Once you are asked back, your performance your senior year doesn't really matter at all.
You graduate, work with them for 2 years or so, and get an MBA.
So what about being 20 makes you think it is unbelievable that I have an internship????