لسَّلاَمُ عَلَيْكُمْ وَرَحْمَةُ اللهِ وَبَرَكَاتُهُ
My sister is 15 year old.
Can she play with a 12 years old boy.
Walaikumussalam w w
Of course not. She is grown up now and the boy is also most probably mature, so she should protect herself properly.