Transferring to the London for college from the United States

Who told you that we start college at 16 in Great Britain?
I guess you confused terms. College in the United States means the university or any higher education. In the UK College is referred to the last years of education in school.
If you mean University, then we start it at the same age, around 18 years old. In case you want to study at the British university, you should come after your final year at school.

College in the Great Britain stands for the high school. You should graduate from the school to study at the UK.
Nevertheless, I want to warn you that it is expensive to live and study in London.

Are you sure that you know all the information to get to the university in the UK? First of all, you should apply for the Admission.
If you want to move at the age 16, how are you going to rent an apartment?
The Immigration Service strictly watches children and will not let you be on your own.
Have a look at the IB courses http://www.ibo.org/programmes/find-an-ib….
It is difficult to consult you on such website, but be sure to visit the following links in case you want to enter the UK university https://www.ucas.com/ucas/undergraduate/…
https://www.ucas.com/ucas/after-gcses

Are you sure that you have enough money to pay for studying and living?
Moreover, do you understand the difference between the high school and university?

The equivalent of the high school is the college in the United Kingdom. University is the higher institution. Students go to the University for two or three years, because they have covered the essential material in college.
To apply for the university, you should take IB and AP.
Visit these pages: http://www.nordangliaeducation.com/our-s… and http://www.nordangliaeducation.com/our-s…
If you are really interested in getting to the British University, you should get better involved in the UK curriculum.

I want to warn you, tell people that you are from Canada.

I am kind of confused.

It will be easier for you to come at 18 as you are going to be an adult.