How early can u apply to uni?

I was just looking through the uni acceptance letters and saw that some universities like Harvard accepts people to be in the class of 2020. (Early action)
Doesnt this mean that the applicant is like 14 or 15 years old?
I dont really understand how this early action works. I thought u cld only apply a year early?

Ok, having googled it, none the wiser, but suddenly thought "class of 2020" might mean the graduation year - so apply one year early, plus 3 three year degree = 2020?

Edit - see
http://news.harvard.edu/gazette/story/2015/12/first-admissions-to-class-of-20/ - it finishes with the quote ".....enjoy your senior year of high school"

You are mostly correct. American universities refer to your class by graduation year and since undergrad degrees are 4 years long the class of 2020 is anyone who applied to start in August 2016, so this current admissions cycle.

Many thanks. So when is the early admissions window (starts Sept 15?) and when is the regular admissions window (starts March 2016?) When would SATs be taken?

Technically there is no starting date as to when you may apply. The things you are talking about (early decision vs regular decision) are not related to when you can apply, rather they are about when the university makes a decision on your application. A lot of universities have restrictions on early decision and in harvard's case it means that if you apply with early decision and get accepted you must attend Harvard. The early decision deadline is Nov 1. In the year before you start. Hopefully this is clear.

You may take the SAT whenever you like except it must be completed by the time you applied to university. You can take it as many times as you like and most students take it once in the spring of their junior year (grade 11) and again in the fall of their senior year (grade 12).

Essentially you apply the year that you are taking University entrance exams.
This is the same for Unis in most English speaking countries.

PS. How are you going to fund a place at Harvard?

They have some of the best financial aid in the world... If people are in families that earn less than ~£45k they get tuition waived, accommodation covered and flights back home.

Including if you are an overseas fee payer? And is this automatic if you get a place? Check carefully. If it was that easy, everyone would be applying for Harvard.

Including if you are an overseas fee payer? And is this automatic if you get a place? Check carefully. If it was that easy, everyone would be applying for Harvard.