I'm going to have surgery to sort scar tissue around my acl is this a severe procedure and will it limit my sporting ability in the future. i'm 35.?

It might: Then again it might help you. It depends upon what is found and what is done about it.

Good idea if stiff: If your knee is stiff after acl surgery due to scarring called arthrofibrosis, a lysis of adhesions+anterior interval release surgery (ie scar tissue release+removal) should improve range of motion and function. Dedicate yourself to post-op pt +range of motion work to optimize your outcome: well-reconstructed acl, +full motion+appropriate, full rehab = sporting ability. Good luck.