"Are youngins really that bad?"
Short answer: No, but sometimes yes.
Many of us got started in cubing when we would be considered 'youngins' and as such we need to take annoyances, fake claims, and exaggerated accomplishments with a grain of salt. I would be skeptical if anyone honestly said 'when I was 13 I never exaggerated.' The first thing I think is important is that 'youngins' are very important for the growth and continuation of our community as a whole. We are much less likely to have someone older start speedcubing than someone young, and the attrition rate for someone younger is much much higher.
If we set aside the 'growth of the community' aspect, what's the value of younger cubers? Young people in general, but especially young cubers have a open mind when it comes to the cube. Things we pass off as silly questions like "Why don't I just solve corners with cross so all my F2L cases are the same" are questions asked by people who aren't stuck in their CFOP/Roux/InsertCommonMethodHere ways. These types of questions provide three interesting benefits, first it allows younger cubers to learn and understand why we follow the methods we do, second it allows older cubers to question their methods and either reaffirm or update, and thirdly it has a (very) small chance of actually shaking the foundation of how we solve cubes today. As humans we don't just naturally do the best thing, in fact we've been shown to do the same decent thing constantly until we finally figure out something better. Younger cubers having a fresh perspective and asking silly questions allows for fantastic opportunity that would otherwise be missed.
So it seems that young cubers are important to promote and can provide significant value to the community, but what about the downsides? Immaturity is the downside most often cited by older members of the community. Their ability to self-regulate their opinions, their feelings, and their personality is very limited, which is a factor of growing up. Some of these growing pains include things like exaggerating personal achievements, faking solves for glory/internet points, and calling other people out/annoying people in ways that aren't considered polite. As much as these things are annoying and it would be great to prevent it, I think it's something that can't really be helped. Every time someone new joins the community, we are adding one more player to the competitive spirit that drives a lot of us to cube. It would be unreasonable to assume people won't crave the attention or good feelings of being victorious when they are in a competitive environment. People (generally younger) who haven't yet decided that there's more to life that others thinking you're cool are more likely to exaggerate, crave attention, and be annoying.
These traits come into more questioning when at an official competition. There are people there of all ages with different goals, different hopes, and different skill levels. A younger cuber might heckle someone faster than them, or try to talk to them over their shoulder during an official solve, or even just shadow them all day. These actions are widely frowned upon by the community (and in some cases spelled out in the rules), but they may just not know better. Education on how competitors should act during competition is something that comes with time, as is having the understanding of how to present yourself and when to keep quiet. We can compound this with 'younger' cubers still going through various stages of mental development, where you start feeling socially awkward, haven't figured out how you conduct yourself in public, or naturally don't know how to make friends.
To discuss the point that younger cubers are questioned more aggressively than older ones I think answers itself. When dealing with someone inexperienced (even if they claim not to be), or even just dealing with someone you assume to be more inexperienced (many fantastic young solvers), your natural instinct is to question, be skeptical and more willing to assume falsity. When someone like Max Park posts a 3.xx solve, we don't question much. When someone who averages 10.xx posts a 3.xx solve, we question a little more, when someone who averages 30 seconds posts a 3.xx solve, we question a lot. This works for factors other than averages too. If someone is new to cubing (regardless of age) we question more, if someone is solving cross on top we question more, if there's any decent reason to doubt the legitimacy of something, we question more. Being young is one of these 'decent reasons to doubt legitimacy' for better or worse.
To end, 'youngins' aren't bad for the community, but there are times, places, and situations where they cause consternation, issue, or argument that would otherwise be avoided.
Chris