I'm considered an adult but i really love to read manga and watch anime, So what about it? People may think that it is childish. They might say that it is irresponsible. You should do what grown ups should do.
Those who criticize you for little things are those that really do not like you from the start, so why care about their opinions anyway. Life is everything but not anothers. do what you love in the extent of your freedom. Manga,anime and comics are those simple and easy things that makes life a little more colorful.