Youth Academy (U4-U9)and Rec (U10-U19) Team Rosters are announced at the end of the second week of practices or beginning of third week of practices once we know the new players a little bit and can place them in existing teams.
We strive to make leveled teams for a more fun game day experience so we give coaches pre-eliminary rosters on the first week of practices so they can incorporate the new kids in the teams so they teams remain balanced as much as possible. It is important you attend practices consistently so we can form our teams as leveled as possible.

For our academy program, depending on the number of registrations for a given season, we may combine U4 and U5 players, U6 and U7 players and U8 and U9 players.
Usually, we have separate brackets for U4, U5, U6 and U7. Each of these brackets were composed by 4 or more coed teams. The U8 and U9 ages were combined but we separated genders.
For our Rec program, typical age brackets would be U10, U11-U12 and U13-U15. Note: we will also have a U16-U19 brackets if we have enough numbers (usually it  will be more likely to have a REC HS age bracket in Spring, as in Fall a lot of players play High School sports).

Why genders together? We have done research and we have concluded that placing genders together in the same teams is beneficial for their development. Here is a nice article by a USSF expert talking about this subject.
In our academy, as numbers allowed, we started separating genders at U8/U9.
In addition, all our U9-U19 competitive program teams are gender specific and teams have licensed, paid coaches.