Denmark is another country with a similar law, which causes a reasonable amount of angst among Danes reaching that age. Particularly true of those with US/Danish citizenship, because once you renounce one or the other, it closes off a lot of options: being a US citizen can be quite good for a lot of career paths, while being an EU citizen can open up a lot of options in a different direction.

edit: Looking into a bit, one thing making Denmark's law somewhat less draconian is that former Danes who lose their citizenship via this process at age 22 still have some kind of special lifetime Danish work/residency permission. So they could opt for the U.S. citizenship while retaining the option to return to Denmark. They would lose the right to live/work in other EU countries under the freedom-of-movement agreement, though, since they'd no longer have an EU passport.