“Allowed” is an interesting word choice.
Minors do indeed have their behaviors to an extent controlled by parents and teachers. That is, boys may indeed not be “allowed” to wear skirts by parental control over purchasing decisions or dress codes in schools. Parents may also abuse children physically or verbally to ensure compliance with gender norms.
At any age, peers and dress codes at work may seek to control the gendered behavior of men. To an extent as we live in a capitalist society no decision can be completely free if the ability to survive depends on it. That’s why feminists argue many women wear makeup or heels mostly because they have to. Same goes for men’s dress codes.
Nevertheless there is no law prohibiting anyone wearing any specific piece of clothing - only norms and financial coercion.
In terms of should they be allowed (original question) I think absolutely yes, and we should strive towards broader acceptance of gender nonconformity in general. Unlike some here I have no problem with drag queens - in principle they are just men in exaggerated feminine attire.