Yes you seem like you will be competitive at those schools. A 770 GMAT goes a long way, so you definitely have that to hang your hat on.
You're right, however in that if you're too unclear about your career goals it could derail your application. Not that you have to know *exactly* what you want to do after graduation. Still, your essays have to be clearer than simply stating that you want the options that an MBA provides. You should craft a story around your career interests. Remember, once you get in you can change your story as many times as you want (and most people do).
Our book is all about crafting your story, so you should get a lot of help from it.
I wouldn't necessarily recommend that you stay away from any particular industry, but make sure that what ever you choose, that you're able to convey a passion for it. Unpassionate applications are often rejected.
The best way for you to combat any weakness that could be attributed to your age is to have a solid story.