1. Still Finding Their Feet: Guys between 20-25 are still finding their feet, hustling, or just not ready.
There are those who are mature beyond their years but those are few and far between.
Ultimately, as a lady in this age range you should be gunning for a guy in his late twenties or early thirties who should be more settled emotionally and financially.
2. Serial Flirts: Guys in this age range are not ready to settle down. It would be quite erroneous of you to take in for them hoping that they may alas settle with you. They would still go on with their philandering ways and might even end up with a lady who is not you.
3. They Are Puerile: They can be prone to making quite juvenile/childish decisions.
These types are still finding their way in life and so errors would be made that transform them into gems later on.