SFML uses internally OpenGL 2.1 (or slightly higher) and no, it's not advised to learn dead old OpenGL. While SFML still uses that old version, it doesn't limit the user to using that old version as well. You can - if you know how and do it properly - use OpenGL 4 with SFML.
For the search, you need to keep in mind, that if you use the search field at the top right, it will search only in the current sub-forums or current thread.
Unfortunately however there still seems to be an issue with the search engine, if the keyword is too common, it will only return one page of results, in that case try to add something additional to the keyword, e.g. "opengl version". I hope to soon get around to fix this issue.