To be honest my ENTIRE tech experience is > 6 years But I know my shyt with the best of them so I'm kind of an outlier when it comes to years experience/pay rate.
There's pretty much three keys to BI Development...
1. Data Discovery and Integration
2. Data Analytics
3. Data Visualization and Reporting
You should have heavy SQL knowledge, data warehouse and database development knowledge (Teradata, SQL Server, Oracal, DB2, Hadoop, Etc.), how to use an ETL tool to move and integrate data (SSIS, Informatica, etc.), how to use tools for data analysis and analytics (SSAS, SAS, Tableau, Excel, Microstrategy, etc.), and data visualization (Tableau, SAS, SSRS, Excel, Microstrategy, Qlikview, etc.)
BI is a very broad topic that requires you to wear a couple of different hats but this ^ is the 20,000 foot overview. You're basically the person that's allowing the company to make data-driven decisions.