Hey there,
Welcome to the forum! You're asking some great questions and let's answer them separately:
1) GMAT: if you're targeting the top programs, your score should start, at the very least, with a 7. It'd be great if the second digit was a 2, 3, or 4. Scoring right at the median for the top programs puts you in good stead, anything higher helps. The average at the top 5 (using US News) is 724. 6-10 boast an average of 716. The 11 - 20 schools have a lower average at 696. You have a pretty strong GPA so that'll help but at the end of the day, the GMAT is becoming an arms race and it significantly impacts rankings. So a 700+ is pretty much table stakes at this point.
2) Now versus 2015: What we advise clients is assess your growth for the next year. Is it going to be linear or exponential? By linear I mean are you going to have job responsibilities and achievements that would be expected of someone in your position and of your age? Or will you be able to do bigger and better things that are usually reserved for more senior staff or older employees? Are you going to rock this next year?
3) Extracurriculars: BUT - you said you didn't have a lot in the way of involvement. So if that's the case, you should wait. Even if you have linear professional growth, meaningful improvement in your involvement will make you a much better applicant. Find opportunities that you are passionate about. Organizations you might have worked with previously or causes you have a history of supporting. Within those opportunities, look for ways to make an impact. Don't just volunteer every weekend at a soup kitchen (although that's great!). But maybe you can help the soup kitchen improve operations or drum up additional donors / support? Find ways to capture scope and then drive impact.
Let me know if you have any other questions!
Bhavik