Is it really difficult to graduate from UCLA in 4 years?

My son is a freshman at UCLA and went in with 14 APs. I believe that translated to about 89 credits. What that means for him is that he is seen as a ‘sophomore’, which helped him NOT being in the last group to register for his Fall and Spring quarter, but being in the pan ultimate group. He was unlucky his first semester at UCLA, when he drew the last registration straw at orientation, which meant that he couldn’t enroll in any science classes (they were all full) and only could take GE classes. He is a double major in Marine Biology and History. He plans to finish in four years, but to do so for his double major, he needs to take 4 courses per quarter, be very flexible as described in previous posts, and attend summer sessions.