What’s the rule on a Senator? Natural born is not a requirement?
Nope. Mel Martinez comes to mind.
Probably a good analogy, though a Governorship is the way you have Arnold S. out in California, so yes, there seems to be different laws for these offices. I think a Senator too, can become one at a younger age than the Presidential requirement of 35 y.o.
That is correct. Only the President and Vice President, need be natural born citizens. Senators must be citizens, but naturalized is ok. But they must have been a citizen for at least 9 years upon election, and they must be at least 30 years old upon election. For Representatives its 25 years old and 7 years a citizen. Both must be inhabitents of the state from which they are chosen.