I have friends who adopted a young girl from Russia and she has ADHD but is doing pretty well.
I know someone else who adopted a 14 year old boy from Ukraine and it seems to be going reasonably well, too.
Is that an exception, or does it happen more, adopting a child of that age?
If I'm right there are age-limits here, to prevent too big problems in adapting. Only on special occasions exceptions are made. (Like when parents are schooled in educating and training kids, and are also adopting a younger sibbling)
I think one can adopt an older child if one wants to. I think that many adoption agencies are more reluctant to give an infant to a couple who is over 45, but there are lots of older childen who really need good homes even more badly. This couple lost a son who had even more severe issues than the child they adopted, so at least they know how to handle a child with severe issues.
I think it would be very sad to be a child in an orphanage who is considered too old to be adopted where you live.
They will make exceptions, but not that easily. It's different from adopting a foster-kid, or a kid you already know. Then these age-limits are not there as far as I know. But when it comes to adopting unknown kids, they do tend to go for younger kids, because older kids have much more problems in adapting, and might be better off in their own country.
The people I know who adopted from abroad are supporting the orphanages the kids came from too. Not only helping their own kids, also those who stay there.