Sure, he’ll never be “locked in” - that’s perhaps a poor choice of words. In my case, I more meant that more effort would be required to change pathways in the short term. For example, as the OP highlighted, the ASN isn’t a transfer degree - so if her son got the AAS and then decided he wanted to major in history and go to a traditional four-year college, he may have some coursework he’s got to make up.
However, OP, with your update clarification (that it’s easier to switch from AAS to AS) and the deciding factors (whether to take algebra II over the summer), I think he should go for it. Accelerating in math is never a bad idea, and it sounds like he has more flexibility than I thought he’d have. He’s at the stage where he has to make more of his own choices, so especially when they are relatively low-risk, I’d let him make them.