It's an a2-adrenergic agonist similar to clonidine. There's definitely evidence it can help with ADHD, but its main use is actually as an anti-hypertensive (by FAR its biggest use in in adults), but it's found some other uses. According to the table on this page
, while all the stimulants are approved in children as young as 3-6 years old for ADHD, guanfacine is only approved for 12 and older, and NOT EVEN for ADHD (this table is a bit old though, as it WAS approved for such just a few years ago, but it's still very uncommonly used). So in short, no, this drug is actually mainly for adults and is in fact used almost solely BY adults.
They can also be doubly useful in ADHD in combination with a stimulant, as they also counter many of the undesired NE effects. Guanfacine/clonidine are also popularly used to counter the unpleasant adrenergic effects of opiates withdrawals. They also help with sleep which is an issue in both cases, as they can be a bit sedating.
However, I've NEVER read anything indicating it has any impact on glutamate, and if I understand the way the article is written, it doesn't even seem to be implying that, but it does it in a horribly unclear way.
I really don't think it has much in common with memantine though... and these a2-agonists have an iffy side too, ESPECIALLY when used with a stimulant. You can develop a dependence to them rather quickly (again, suggesting it doesn't really effect glutamate much if at all), and simply forgetting to take your dose can cause your blood pressure to spike dangerously high. Concurrent use with a stimulant like it's often used with ADHD can make this problem even worse. Personally, I wouldn't want to be on the stuff long-term.