How many years old does something have to be to be considered an antique?

Antique is not about age. It is about market. If something is 2 years old and not available on the market any more, it is an antique. But, if you are talking about really old stuff, then the rule of thumb is that it is something that was created at a time when the technology of a certain time-period was unavailable. The more basic the tools of creation, the greater the antique value. So, 20th century is antique, compared to 21st century stuff but 19th century stuff is more antique than 20th century and so on. However, if a 20th century artist is creating something using only 12th century technology, he is not creating an antique. Once you go beyond a certain time period, (more than 10,000 years ago) anything and everything is valuable.