Now that we have a little more to go on, he can certainly be a candidate and you will see a little bit of a % boost going ED, but I think the odds are still against him with the ACT, but they have admitted people with 29 so there is a chance with a really good essay that clearly demonstrates why Cornell is the best place for him. I applied ED last week and have slightly better stats but not much. But I’m also a realist and turned in 5 other applications for early action just in case. I still have 4 other schools I will apply for in December - making 10 total application with just the one ED. I’d be perfectly happy with my #2 and #3 choices and they are both in the target/low reach area.
Point is, if cost is no issue and Cornell is his absolute #1 choice, apply ED. Even if the chance is 20%, that’s still better than zero and the only thing you lose is the application fee (and the chance to apply ED somewhere else, but that doesn’t sound like something he’s interested in). Good luck.