Does it still make sense for him to learn Flash? And if not, what tools should I be steering him towards instead?
Here's a link, and all I see is an offer for a 30 day trial: http://html.adobe.com/edge/animate/
The word "trial" is not something I associate with "free".
And before you mention Adobe's Creative Cloud product, let's try to be pragmatic about what "the cloud" really is. It's not something you ever really own, because nothing in "the cloud" is ever really "yours". You never honestly have control over something when it's on someone else's server, and they're paying the power bill. And truthfully, if you have to pay for an always-on internet connection, in order to take advantage of a software-as-a-service, the main drawback is that's the software is only as reliable as your internet connection, but not only that. There is also the demand that every system between you and the server hosting the SaaS must also function flawlessly, or you risk losing your work.
Not to mention the nature of secrecy and intellectual property rights, and "stolen" artwork or "ideas", regarding "the cloud".
1) As a platform Flash may yet survive the web, Adobe has real potential transforming it into a publishing tool rather than publishing + consumption.
2) Adobe themselves are likely to keep their throne in the tools scenario and they probably won't deviate far from the methods they and Macromedia have spent 2 decades discovering / implementing / selling / training people to understand in Flash.
The best although short-lived reason is Flash is a very rewarding platform to work on, there are eleventy billion tutorials and your brother will probably have some simple animations working on day one and that sense of accomplishment is invaluable.
Their 'open-sourced' tools haven't been updated for the last few years. The most recent Flash 'roadmap' doesn't actually lead anywhere. Finally, Adobe's Thibault Imbert admits that Adobe is now focused on javascript and HTML5: http://www.bytearray.org/?p=5197#comments
Basically, Adobe has quietly abandoned Flash, leaving behind a bunch of bitter developers.
If your bro wants to make fun animated cartoons, I think it's a great way to start. He can also learn little bits of scripting, using ActionScript 3.
The other interpretation of "should I learn Flash" is "should I learn ActionScript 3 & Flash Builder (Eclipse)?" You can use AS3 and Flash Builder to make web apps, along with really intricate animations or video games. This is a tougher question, because many people are moving toward HTML5 nowadays.
However, if he wants to make simple videogames, I still think of AS3 as a good way to learn programming! In syntax, AS3 is very similar to JS. However, AS3 also includes a static/strong type system, which is a nice way to ease into "scarier" languages like Java and C++ and Objective C.
AS3 has a nice method for loading & animate sprites. It also has many 3rd party libraries. AS3/Flash also handles sound effects for game audio pretty well. If he wants to distribute his game to his friends, he usually doesn't have to worry about cross-browser issues. :-)
There are also a few inexpensive Html5 animation tools such as Sencha Animator, A5 and there are a couple others you can search for. I tried Adobe Edge animate and I didn't like the folder structure it generated, but that's just me probably.
My view is the Creative Cloud subscription model is a mistake and I don't plan on buying into it.