Is it permissible for me to be breastfed by my maternal aunt when I am 21 years old, knowing that the milk is hormone-induced?

"Radha'ah Kabeer" (adult suckling) does not establish prohibition. As for an adult drinking a woman's milk without necessity, there is a difference of opinion among jurists, with some prohibiting it and others permitting it. However, if the drinking is directly from the breast, this is impermissible because it involves touching the 'awrah (private parts) without necessity.