Great kid.
Sorry to add this realistic counterpoint, but it may help him narrow down college targets.
No idea what colleges you have in mind. If by “top” college, you mean a holistic most- or highly-competitive (let’s say top 25,) does he have any math/sci ECs? These schools will look for that sort of experience, testing his interest, and especially for engineering, the collaborative mindset certain sorts of activities show. Even “tinkering.”
The problem is the fierce competiton from other kids who seemingly did it all. There will be many great engineering programs that won’t expect this. Others can advise you on those.
It’s not as simple as Eagle vs 20 hs clubs. (And the impact of Eagle depends on his project.) The top colleges will want to see interpersonal/peer skills and other attributes, as well. If he’s a junior now, he could find a way to fine tune. Look at what the colleges say they value and “look for.” This is’t about helter sketer piling on clubs. It’s about reflecting what improves your shot at a “top” college.
Look at the Common App, look at supplements from various colleges he may be thinking of, see what they ask. And see if some have an additional engineering supplement.
Best wishes.
ps. If you’re worried some college may see an issue with “suddenly” signing up, consider how they react to the opposite: not having the right range of ECs that show what they need to see. It’s far risker to assume joining the right things, getting in some comm service, etc, is “padding.” I don’t know why so many assume valid experiences would ever be dismissed.