I'll go through the items you mentioned.
1. 20 weeks would definitely be reasonable.
2. No, the agreement doesn't prevent you from claiming California State Disability benefits.
3. Yes, commission being part of your severance would be reasonable.
4. Medical insurance for length of your severance--not sure what you mean. You're only being offered COBRA coverage, which every employee has a right to anyway, and your employer cannot extend your eligibility for that coverage. If you want health insurance benefits paid by the company, you need to negotiate for that.
5. I doubt they'd be willing to match your 401k contributions now that you are no longer with the company, so I doubt they'd agree to that provision.
If you believe that your age was the primary factor in your termination, you should not sign away your rights to sue under the Age Discrimination in Employment Act, since you could potentially receive 10s of thousands or possibly 100s of thousands (less likely) from a successful claim.
Unfortunately, if there were any other issues with your work or anything else, your employer would probably defeat your cause of action, so you definitely shouldn't base your decision on the amount you could get from an Age Discrimination law suit.