Complex sentence: Associations affiliated with FIFA were invited to send their senior women's and men's under-23 national teams to participate; men's teams were allowed to augment their squads with three players over the age of 23.
Split into simpler sentences: Associations affiliated with FIFA were invited to send their senior women's and men's under-23 national teams to participate. Men's teams are allowed to augment their squad with three players over the age of 23.