Are you being unfair to judge 'some' of the guys your age as immature? Nope. They very well may be immature. Even if they aren't really that immature you are free to make your own decisions about who you find attractive and desirable.
However if you want to date in this age range and find that NO men in that range are desirable I would question what is causing the problem. We have 4 options:
1. There are legitimately no 25+ men available who are mature/wanting to settle down [This seems unbelievable as lots of men do marry in this range and even become active fathers.]
2. You are looking in the wrong places for men. [Decent possibility, dating apps and the like are miserable places too look]
3. You are looking at the wrong men. [The most attractive people are likely to be tied down if they are looking to settle or be making use of their attractiveness to 'enjoy their youth'. No one wants to date an uggo, but the people who have the most experience with getting the opposite sex's attention are going to be the ones that stand out most.]
4. Your standards are skewed [Perhaps older men aren't that different as a whole, you are assessing men who are married and professionally established.]