Personality, sense of humor, and similar interests along with sexual compatibility all factor into a man's decision to stay with a woman or move on. Another important thing is (timing).
Most men are not ready to settle down or get married until they are close to age 30 or beyond. Unlike most women who as girls played with dolls, feeding them, changing their diapers, pushing them in strollers, cooking cakes & pies in their Easy-Bake oven and decorating Ken & Barbie's house, while dreaming of being a princess...etc
Men most likely have (never practiced being a father or husband during their childhood) or formative years. Society has not imbeded it into their subconcious. Therefore it takes decades for a lot of guys to start thinking in those terms. He may meet the "perfect girl" at age 23 but he is not likely to be in a rush to become like his parents. A woman in her 20s who has her heart set on getting married would probably do better dating men in their early to mid 30s. One man's opinion! :-)