Can girls play in mixed teams, and up to what age?

Yes. Under FA Rule J3 (2026/27 FA Handbook), players in a match must normally be the same biological sex, except:

1. Under 7 to Under 18 inclusive: mixed football is allowed in every youth age group, so girls can play in mixed teams right up to Under 18.
2. Mixed adult football in competitions authorised by The FA. You must be 18 or over to register for or play in these.
3. Players eligible under The FA's policy on the inclusion of transgender and non-binary people in football.

So once you're past Under 18, open-age football is played in women's teams and competitions, apart from FA-authorised mixed adult competitions.

Mixed teams follow the same formats, laws and age-group rules as everyone else in that age group.