Vegetarianism has been around since ancient India and Greece. I have several friends who are vegetarians and say they love it.
Are there health benefits to it? 
Some think abstaining from animals does lead to health benefits but most vegetarians do it out of respect for life.
What do they call people who do it based on mental issues? Like meat makes you queasy. 
I don't know if they have a name but there is a field of research in the psychology of eating meat.
When does it date back too?
History of vegetarianism
The earliest records of vegetarianism as a concept and practice amongst a significant number of people are from ancient India and the ancient Greek civilizations in southern Italy and Greece. In both instances, the diet was closely connected with the idea of nonviolence toward animals (called "ahimsa" in India), and was promoted by religious groups and philosophers.
Following the Christianization of the Roman Empire in late antiquity (4th–6th centuries), vegetarianism nearly disappeared from Europe. Several orders of monks in medieval Europe restricted or
who do not, and it has been applied by animal rights advocates as well as by ethical vegetarians and vegans.
Ethical vegetarians say that the reasons for not hurting or killing animals are similar to the reasons for not hurting or killing humans. They argue that killing an animal, like killing a human, can only be justified in extreme circumstances; consuming a living creature just for its taste, for convenience, or out of habit is not justifiable. Some ethicists have added that humans, unlike other animals, are morally