Mainly the result of societal pressure or expectations. Being a 33 year-old man, never married. That's "normal". If I were a woman, people would be asking me when I was going to get married and have kids (very much depends on area, but this is not at all uncommon). As a 33 year-old man, it's also not thought of as strange for me to date women in their early-to-mid 20s. The same is not true for women my age.

Then there's also just how people tend to rate attractiveness, which is something that really matters in a lot of these online dating systems. Men are generally viewed as (physically) attractive at higher ages than women are. A few wrinkles on a guy, some gray. That makes him "distinguished". You don't here people saying that about women as often.

The age range and feature-sets for what makes women attractive (again, this is emphasizing first impression attraction) are much narrower than for men.