Most Helpful Girl
I think those changes happen as we move further into or closer towards adulthood for a few reasons.
For one, men and women become more mature. Playing games, being manipulative just for attention or to get one's ego strokes are seen less and less. That's partially because of the second major factor, that as you get older, both parties start to know what they want more clearly. There's less of that 'I'm not ready to settle down' or fear of commitment.
Many will be more clear in knowing that they want a long-term partner, hence making them a lot less tolerant of people who play shenanigans. Having a goal towards they know they want to get closer will make them put more effort into looking/behaving in a better manner.
(I do think these changes or a general turned including them does happen for many people. Doesn't apply to all, as some know they want to settle down from the get-go but it would be applicable to those who are one off those 'bachelor for life' types when younger, only to realize that it would be beneficial to have someone to offer companionship among other things to them as they age.)
Most Helpful Guy
Women's power in the dating world is rooted in her looks and sexuality. When they are young they have the advantage. A 21 year old woman is desirable to men rnaging from 18 all the way to 40.
So a young woman has a lot of options and only faces serious competition from other young women. A 21 year old man has to compete with other 21 year old men as well as 26 year old men who are more established and potentially more attractive since they'd have a more mature look.
When women get older, start to lose their looks and become more desperate for commitment, they lose somw of the power they had. Men become more established in their careers (something women find attractive) and the power dynamic starts to switch towards men's favor.
Bassically both genders have a prime where they will peak in desirability snd have the most options. Then they start to decline. A womans prime is around 22 while a man's is around 26. At 26 you have that balance of looking mature without being looking too old and at the same time you are more stable in your career, both of which make yu desirable to women from 18-26 versus when you were 21 you were mainly desirable to other 21 year old. So you appeal to a wider demographic than you used to.