Well, I persoanlly don't think it's right for an establishment to price their product differently to people just due to a demographic.
For this reason, I oppose senior discounts.
To me... ideas like "skirt nights" that give the discounts to anyone wearing a skirt are a lot more fun, not based specifically on a demographic (man/woman/age...) and accomplish much the same result.
However, as much as I may not like them, there is no requirement for someone to go to a specific bar/nightclub on a given night, so government has no place getting involved in this issue.