Thank you for your responses. I will pass on your advice to my son.
Why triple majoring- He was torn between majoring in math and physics when he started last semester, so decided he would double major. He then told us part way through first semester that after completing the math and physics majors, he would only need to take a few additional courses to add a major in computer science, which he also enjoys.
He will be through all calculus/multivariable/linear algebra/discrete math courses and the gateway courses for CS and Physics (+2 physics quarter electives) after this semester. The open curriculum only requires minimal distribution requirements and he told us he may try to even get some humanities and social science courses done in summer session so he can do more STEM classes during the school year. We are not pushing him, this is all him. We told him to follow his interests and adjust his plans if his interests change, the work became too overwhelming or he wants to focus more heavily on any of the potential 3 majors. He is enjoying and doing well (Dean’s list) in his classes, and has time to hit the gym every day and play intramurals and a 2 season club sport, but I will be happy when he gets official major advisors to guide him next year to make sure his course choices present the best for any future studies.