Absolutely agree. One cannot start too early. Academy Days are great places to meet ALOs/BGOs/MLOs. Check in with them. Know who they are. A "check back when you are a junior" remark, however, must be accompanied by a "put yourself in the position to take the highest level math and science courses your school offers" comment because the end of junior year is too late to cram in AP Chem, Physics, Pre-Calculus, Calculus, and a few others.
A jaded observation is that a lot of my pre-junior year contacts seem to be Academy Day attendees who have heard the above remark who are looking for my support in their rationalizations, excuses, and reasons for not taking calculus.