It's a rolling admissions process, so the later you wait, the more competitive it gets. Usually, around 5000 apply, and only 260 applicants are selected for each section, so about 5%. However, it's unclear if the 5000 is for all sessions, not just one, in which case you jump up to about 16% acceptance rate. Regardless, go ahead and apply! Make sure to nail that personal statement, and make sure each of the 1000 characters has a purpose (except for of course the spaces that are counted). The lack of test scores might hinder you, but as long as you have a competitive GPA and class rank, you should be ok as long as you nail that personal statement and are involved in extracurriculars. Again, these are outreach programs and aren't designed to indicate that you're going to be accepted when the real application comes around next year for you. It's a great program, but it is by no means make or break. Do your best, and start preparing for the Summer Seminar App next year! Hope to see you at the rising Juniors session for STEM!