I guess you're talking about the aircraft pilots during WW2. The Germans called them "Experten" (experts, not aces) - only single counting of kills was allowed in the Luftwaffe.
Well, it's not easy to say how many victories were necessary to become an expert... the German Luftwaffe had several pilots with far more than 100 kills at the end of the war. The best two surpassed 300 victories. It is assumed that German Luftwaffe officers adjusted the required amount during several periods of the war... I didn't find any exact number.
5 kills without dying
"How many years does it take to become a chemotherapist?"
How many years does it take to become a cytopathologist?
2 for a UAV, 3 for a Counter-UAV
how long does it take to become a gerontologist?
i belive almost 200 or 400
Just one, but the enemy has to be lunging at you with a sword.
750 points, 10 points per kill, so 75 kills
it will take 8.5 hours it is 740km if you use E30
1-40 times easy
How many years does it take to become a genetics if you start from AA degree?
he is an anarchist that kills people just so batman will give up and take off his mask. he kills many in gotham to prove everyone can fall hard in life.