Please
Use Code Tags. It preserves the formatting. I've added them for you this time.
First, let me help you with some logic errors.
Use equals to check for equality. == checks if two references are pointing to the exact same object. This is rarely the case, even with strings. equals solves this for you:
or shorter
By the way, the female percentage will always be used because it's spelled "male"
Both will return 0. This is because 20/100 and 18/100 are both 0 - integer division will not return a float or double. Instead, turn one or both of the operands to a double by appending .0 to it:
Now if I were you I'd go for option three. What if youths only need to pay 15%? You don't want to add a third method (option 3). That leaves options 1 and 3, but option 1 uses strings to determine the type. As you've already made a mistake in your code, it's quite easy to have the wrong tax amounts determined. If I even passed "Mail" the method would regard me as female.
One final note: using float and double will eventually lead to rounding errors; that's just how floating point calculations work. You can see it even with a simple example:
Since your calculations are about money, you can't afford such errors. java.math.BigDecimal is a better solution then.