Disclaimer: 21 and 22 year olds might not like some of the things I say, and that is okay. Feel free to call me a misguided old man to feel better. Also there are some generalizations involved, some may apply to you more than others. The take away message should be that for most of these things, you're at your worst at this age. For example, you may not be selfish, but your selfishness will be at it's highest at this age.
They old adage that "Youth is wasted on the young", often seems true in regards to 21 and 22 year olds. Obviously ignore this if you're in that age range or younger (you won't appreciate the rationale), this is advice for mid to late twenties. Date people in this age group with caution because they're extremely dangerous or reckless or some unpleasant combination of both. 21 and 22 year olds have their strengths and weakness just like any other age group, but if you're in your mid-twenties you probably won't like what they represent. Let's be honest, they represent a younger version of you, going through stages and phases you've already experienced. I wrote this based on how I perceive their actions and my reflections on my own time as being 21-ish (let's call it that so I don't have to keep typing 21 and 22 year olds), you may have a different perspective. Don't mistake this post as me saying they're bad people, which is not my intention at all. My rationale is that the 21-ish crowd can be extremely difficult for anyone that is not in that age range. It's like they have a code of conduct and ethics that only makes sense to them.
Why is this group such a hassle? There's literally probably hundreds of acceptable reasons (okay I'm being dramatic), but I'll rattle off a few that comes to mind. First and foremost, they're just coming into their own. 21 and 22 is a very important age as far as growth and maturity goes. For a majority of people it is the first time they are really an adult, and the wisdom increase from 18 to that point is immense. The problem is that too often 21-ish year olds believe that because they are a lot smarter than they were at 18 that they've transcended to another realm of intellect. They display this in an arrogant, entitled, and condescending fashion, which is unrealized to them but former 21-ish year olds know exactly what I'm referring to. They also couldn't be more wrong; they'll have just as big of an increase in wisdom and maturity between 21 and 25. You cannot tell them that now though, because they're 21-ish and already know everything. Related to this is the fact that they take themselves way too seriously. What I mean by that is they're rigid in their wants and expectations and leave little room for flexibility. Controlling how they come across is more important to them than actually being happy. Just such pretentiousness all around, and I understand why but they will realize in a couple of years just how ridiculous they were. A favorite quote of mine is "When you're stubborn and prideful, not much is insightful". I don't think you can possibly describe early twenties better than that.
Another thing that makes dating the 21-ish group hard is that they think everything is replaceable. At 21-ish you always feel like if you have something good, you could always get it again or obtain something even better. A person with that mindset is dangerous. That type of person might not see the errors in their own ways nor bother attempting to fix them. Instead of being self-critical and actualizing, they can just chalk any loss up to the game and move on. They often brag about this (their ability to "cut people off"). Part of that is because they stay in a comfortable bubble (if they're college students). If you're 21-ish, you are probably an upperclassmen and part of the highest social status in that bubble. That's a very exclusive club. For females it's an absolute position of power and they rule as such, like absolute monarchs. At that point, you're in a familiar environment and if you are attractive, there's literally hundreds (maybe even thousands) of people in a 10 mile radius that would give you the time of day. On top of that, they'll draw interest from men age 18 through 30. This means that they will always have a plethora of options and never have to take any responsibility for relationship failures if they don't feel like it. That's not bad for them at all, for someone older that likes them, that's equivalent to playing with fire.
Then you have the proverbial "late bloomers" even though this age isn't really late bloomer age quite like late 20's. Well these are people who are newly attractive and you can expect them to respond as if that's the case, unpredictably. Being a "late bloomer" affects people differently and you never know how it may affect the younger person you are interested in. I know a few "late bloomers" that are 21-ish that are purposely sabotaging any and all relationships because the new thrill of being wanted is too exciting to them. Of course they won't say that, and there is nothing wrong with them taking advantage of it either, but if you're the older person that likes them that's something to be mindful of. They also won't learn this until later, but the brashness of flaunting how much you're wanted is unflattering. You don't have to make it known every five minutes, how many people want to talk to you. In my opinion 21-ish is also the most selfish years. Now there's a big difference between selfish years and someone that is just flat out selfish. Knowing that difference can save you a headache down the road. 21-ish year olds aren't selfish in a bad way per se, but like I mentioned earlier, they are just coming into their own and are more likely to place a disproportionate amount of emphasis on their own wants and needs over yours. Anyone with experience knows the struggle of relationships without balance, and that's something you're signing up for with this age group whether you want to or not.
Lastly, the 21-ish crowd are prisoners of the moment. Immediate wants, and instincts always seem to override their rationale, and that rationale may not have even been rational to begin with. This may be the most damaging as far as preventing good relationships. It makes them very susceptible to dangerous swings of highs and lows. Now that's not to say that older people perfect in this regard, actually far from it, but at least then most actions and decisions are based on some sort of logical plan lessening the collateral damage. Not the "it feels good or right, so I'm going to do it" type of plan either. Instincts are very important, but you also have to learn when not to follow your instincts. People also become a bit more predictable with age. Some level of predictability in dating is a good thing. Spontaneity may be more exciting, but it can also be more stressful. Sometimes it's good to know how that person will respond to certain things. Every decision in a successful relationship can't be a risk.
Anyways, try to avoid dating 21 and 22 year olds. I know it's easy to be drawn to their "potential" or the fact that their sporadic behavior can be exciting at times, but trust me on this and just let them be. They're like that free spirit that is meant to be admired from afar or that beautiful flower that you should leave in the ground after smelling it. They're just not ideal for dating, not yet but they will be. Take solace in that.