Using a 12 Mhz xtal clocking the chip to 100 Mhz.
Why says that you have to use a 12MHz crystal?

And, there 24 'Mhz' written on the chip, can we clock up to 100 Mhz?
Of course not, you will need another derivative.
1) you can only clock a chip up to its Max frequency.
2) the Cygnal f12x has a max frequency of 100MHz.
3) most high clock frequency derivatives have an internal PLL multiplying the clock.

Erik