Friends are not only the human beings, they may be animals, things, nature, spirit or god. They may not be have same age group or gender. They may not be alive. They may not be speak with you. They may not be visible to you. They may not known to you. They may not do anything to you. But they always with you, do not harm you, help you, accompany you, they do whatever you want, but you do only one thing. That is mind this universe as friendly.