Creatinine levels relate to both muscle mass and to kidney function. As you age, your muscle mass decreases but your kidneys tend to function less effectively. The net result is not much change in creatinine levels in the blood as you get older.
As a result, California employers are required by law to have workers' compensation insurance, even if they have only one employee. And, if your employees get hurt or sick because of work, you are required to pay for workers' compensation benefits.
Second, workers comp is not going to pay you 100% of your regular wage whether you have vacation or sick time to apply or not. I'm not sure how they do it in california, but in every state I have worked in worker's comp only pays a percentage of your regular pay, usually around 2/3 or 66.6%.