- Brand new domain with no domain authority yet? 6 Months for a competetive term?
- Site black listed?
- Site has errors on it and can’t be crawled (robots.txt file sitemap.xml file – Google Sitemaps account will tell you)
- Site is not search engine frinedly.
Your doing something wrong if you have not seen any results in six months… Even with a super competitive keyword you could move in 6 months.
But like everyone else said it depends on a lot of thing like how well your ranking now how much better those ranking above you are doing SEO. The difference between your linking profile and those ranking above you.
The list goes on and on without detail your asking us an impossible question.