An effect such as you describe certainly exists to some extent. I don't know from personal experience if it's as large as you say. (I suspect it varies a lot across different cultures.)

The question remains: when 21 year old women see that only men who are at least e.g. 25 years old are attractive enough for them, do they consciously rank attractiveness by age, or does age translate into other objective attributes like e.g. experience?