Clarification on what the max freq of PIC24FJ64 is?
The datasheet is correct, as they usually are.  The PIC 24F family can run at a maximum instruction cycle rate of 16 MHz, which can be expressed as 16 MIPS (Million Instructions per Second).  This processor requires 2x clock over the instruction rate, so the maximum clock is 32 MHz.  You can achieve 32 MHz clock with a 8 MHz crystal and the 4x PLL.  That will result in 16 MHz instruction clock.