Hi and thanks for your post.
You have an interesting profile and it's nice to see you have thought a lot about the application process.
As you mentioned, the average age is closer to late 20s, so the key is really convincing the admissions committees why it makes sense for you to now get your MBA. This is where your essays are critically important. And yes the fact that you have a guaranteed job lined up upon graduation is definitely in your favor.
I agree that with a 710, as well as strong leadership experience at work, it is worth applying to a full time program. Harvard and Stanford are reach schools for almost everyone, and since their average GMAT is 730+, that is the case here. Sloan, Booth and Haas have averages around 720 so I agree that applying to a couple other schools is a smart idea. These top schools are all so competitive that they can't admit all the qualified applicants, even those with extremely high GMAT/GPAs.
I feel that your work experience can help differentiate you, so hopefully you will be able to elaborate on compelling leadership experiences where you really made an impact on your teams.
Good luck and let me know if you'd like to sign up for a free consultation to discuss your story.