Random Forest: how efficient is it for features in a range of values (not binary thresholding)?
Is it correct that each feature is only used once in one decision tree?

No, if the variable is a continuous value like age, it can use threshold splits at each level. So, same feature can be used multiple times in any given branch of the decision tree.
And since the random forest is nothing but collection of decision tree it follows the same principle.
Reference