Gender imbalances are more dramatic in the 20-60 population than 0-20 because children have less say in where they live. In other words a 32 year old male might decide to move based on a gender, but people rarely move based on the gender of their children.

Also, a high percentage of dating age people are in a relationship. If there is a 48:52 gender imbalance in 25-45 year old population. And 2/3 the women are in a relationship (ignoring the same sex relationships) the gender imbalance is more significant among the single population. 48 /3 vs 52 - (48*(2/3)) is 16:20 or 44.4:55.6