Medicare like Social Security is intended for retirees.  You pay into the program while you are actively employed and when you reach 65 years of age you start to receive Medicare coverage.  However, the coverage is only for Part A.  If you want clinical coverage for minor health problems you pay for Part B or choose an Advantage offering from a private insurer.

To include immediate health insurance coverage under Medicare for active workers the whole program needs to be overhauled.  It's not impossible, but the payroll deductions would not be  affordable, in the hundreds and possibly over a thousand for spouse and children coverage.