How do u know whats your grade in playing the flute, and how high do the grades get, and whats your guyes grade and how long did it take u to get there.

There is no sure way to know until taking a graded test like a board exam.
Your teacher can normally give a good estimate based on your playing abilities and whether how good you are at sight reading.
you also need to know the relavant scales and arrpegios for that grade

in england it goes up to grade 8 and then diplomas etc it`s taken me 8 years to get to grade 8