Hi Silver. I see this alot with kids wanting to start out in OL. This site has excellent stretching recommendations, see the EXRX Muscle and and Exercise portion here on the site. Sretching aside, here is what I recommend; get an empty bar, or PVC, or a wooden dowel, and work on 3 movements for hip, ham flexibility. Overhead squats, front squats, and the RDL stretch. Do them daily, several times daily. Don't worry, it won't cut into any mucle development as there is virtually no loading. Try to continuously get deeper. How long will it take? I have no idea, it varies from individual to individual and how tight you are, and why you are that way. In my case, it's osteoarthritus,and it takes a long time. just don't be discouraged, just work on it.