The length of a personal injury case depends on many factors. It depends on when your medical situation becomes concrete relative to the time of the accident. It depends on how motivated the client is to achieve quick closure in the case, versus allowing time for all of the evidence to develop. It depends on how much investigation and discovery needs to be done. It depends on the reasonableness of an insurance claims adjuster or defense attorney. It also may depend on how backlogged the court system is when your case is filed and ready to go to trial.
Your facts and circumstances are completely unique to your situation. For a more realistic estimate of what a timeline may be in your case, you should speak with an experienced personal injury lawyer.