<p>Colleges have admitted freshmen who are under 18 years old for a long time. They know the various accommodations needed to ensure a safe and beneficial transition for those students and their families. Often, they are housed with 18 year olds — and no issues usually emerge. I do recall Yale mentioning somewhere that they had concerns for students who would not turn 17 years old some time during their Freshman year – implicitly this means they have lots of experience with 17 year olds turning 18 after matriculation. But to the OP’s question: no it does not ADD anything to your file. Indeed unless your ECs and other accomplishments are on par with your 17-18 year old competitors, you’re at a disadvantage.</p>