I would concur with Mr Modesto's comments. You may also wish to consult a physiotherapist and ask them to suggest some small changes to your warm up routine to minimise any impact on your knees while still retaining the benefits of your warmup routine.
About 15 years ago I've had a series of hyperextension injuries to my left knee that resulted in some cartilage, tendon and ligament damage (some of which is permanent I think). There are days where the knee aches and there have been the very rare occasions where it has locked up. Sometimes I have to use a knee brace to train and sitting in sieza can be uncomfortable at times.
I think with careful and considered management (including medical advice) of the condition it should not pose a problem for your training.
I've been training in aikido for 9 years now and prior to that 4 years of jujitsu. Yes I do have some problems with my left knee but the precautions that I've taken havent put a crimp in my training. For the record I'm pushing 40
All the best for your training.