you may switch.
Do consider all the factors involved though:
Whether all the schools you're interested in accept the GRE score, whether the industry in which you want to land up post your MBA looks at your GMAT score etc.
Personally, I think there is not a lot of difference between 660 and 700 and the jump is achievable. Also, at 30 you are definitely not too old. There are a lot of 30+ applicants each year.
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