This is actually very easy to answer and vag is getting decently close with his post.
Yes, it might be more difficult for one guy than for the other to increase his squat. We do not even have to get into the height and levers debate, individuals just vary in their abilities, period. But every healthy male under 40 has a very decent chance to reach the rather modest goal of a 2x bw squat IF he is willing to gain the necessary bodyweight to accommodate serious training and improvements.
There are gifted people (A) that do not need to gain ANY bodyweight to achieve a 2 x bw squat in less than 6 months. If you are that person, congrats to you, you lucked out in the genetic lottery. But most people struggle with that, HARD (B). They increase their strength, sure, but it takes them ages to get to decent levels because they insist on staying skinny. If you are that person, you are making life more difficult than it needs to be. More importantly, you are wasting very valuable time because it will certainly not get easier to achieve your athletic goals with the years.
There are basically two options if you are type B: You can creep forward 25 lbs in the squat per year while not gaining any bodyweight and maybe, MAYBE someday achieve your strength goal that way. Or you can make the reasonable decision and begin eating like someone that trains HARD and have a 2 x bw squat in a couple of months - guaranteed. Sure, you will be heavier. Sure, you might not see your abs anymore. But you are also much, much stronger to move the bodyweight around. 200 lbs is not a high bodyweight if you squat 500, is it?
Now, what is holding people back? It is a lack of realistic self-assessment of ones own talent (for example in regards to strength) and not doing the things that would logically correspond with such an assessment. In other words, if you are type B and make yourself believe that you could be type A, then you will be the guy that has a really, really hard time getting a 2 x bw squat. For everyone else, this is just an increment that comes and gets surpassed rather soon.
I heard that you should squat max about 2.5x bw else if you exceed that then you will start to slow down as you bulk up. so wouldn't squatting 3 or 4x bw slow you down.
There are maybe 5 people on this forum that get close to this number. I would not worry too much about slowing down after the 2.5 mark because you have to get there first.