I don't think you're too young with three years of full-time work experience, although I noticed that the schools that these days most seem to prize younger applicants (like HBS and Stanford) aren't on your list. Anyway, I don't see a need for you to wait abother year or to, simply for the sake of having a little more work experience when you apply.
Your overall GMAT score (710) is fine, although it also depends on what your quant/verbal breakdown was. If either score was below the 80th percentile, you may want to try again, just because you have the time to do so (I assume you'll apply in fall).
Two other thoughts: Since you were a marketing major and didn't have a super high GPA, consider taking a college course in calculus/stats/econ/finance (unless you already did a lot of that in college), just to show that you can handle the more quant-heavy work. Also, you mentioned that you plan to keep working for your company... That would be best for a part-time program. Full-time MBA programs don't really want to hear that you plan on giving them anything less than 100% of your full attention!
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