I was wondering why big german aces shot down the most enemy aircraft while fighting on the eastern front. Is this because the soviet pilots were undertrained, or their flying machines were inferior? Is it something else? You see all these German aces that have shot down 100+ aircraft and most of them fought on the eastern front. Why is that?
Several factors. The ones you mentioned, plus the different purpose of most of the Soviet aircraft and the longer flight career of German pilots on the Eastern Front. Beyond that was the fact that, early in the war, the Germans enjoyed near-complete air superiority (reinforced by their superiority in other factors).
As you note, at the beginning, most of the Soviet aircraft were inferior to the German ones; some of them were ten or even fifteen year old designs (or even older -- one squadron, known as the "Night Witches", flew biplanes into 1943), while the Germans flew new designs, either late pre-War or fresh off the drawing board. The newer aircraft were faster, more robust against damage, carried heavier loads and more/larger guns. This aircraft design deficit was reduced and possibly even reversed later in the war, but by then the Germans were on the defensive, being pushed back week by week.
The German pilots, at least early in the war, were far better trained -- theirs was the best air force on Earth in 1940 (though they started to run out of good pilots later in the war, because they had a far smaller population to draw replacements from and were resource limited in building aircraft, both for combat and for training).
Further, the German aircraft that the aces flew were dedicated fighters, designed from the ground up to destroy other aircraft in the air. The BF-109 and Focke-Wulfe 190 were superb airplanes for the day. The Soviets, on the other hand, especially early in the war, had a heavy preponderance of ground attack aircraft, and their primary mission was to destroy German armor, infantry, and supplies. This made them sitting ducks for the German fighters and fighter pilots. Further, there were lots and lots of those differently tasked and outdated Soviet airplanes -- the Soviet Union had more than twice the population of Germany and tens of times the landmass and resources; that gave them the ability to do the air equivalent of "human wave" attacks, which would still succeed even after a "turkey shoot" by the Germans.
Because of the disparity in pilots and aircraft, the German pilots lasted a great deal longer on the Eastern Front, where they weren't flying against the elite of nations larger than their, who hadn't had a decade or more with no powered aircraft and who had P-38s, P-47s, and P-51s, Hurricanes and Spitfires to pit against their aircraft. The Western Front pilots had a strong tendency not to come home, even in the early years of the War, and much more so after the Normandy invasion.
Additionally, especially after the first winter of the Russian invasion, German pilots stayed on the line until they were physically incapable of flying -- either dead, or seriously injured (loss of eyes or limbs, for instance), or shot down behind lines and captured. As noted in comments, also, there was a tactical difference, with German squadron leaders often flying without any thought for defense, trusting their mates to protect them while they simply destroyed as many enemy aircraft as possible, and this worked better against the relatively less experienced pilots in the Soviet forces.