Take percent from the father – how to calculate SF?

Hello, my current vehicle is admitted to me (so I’m the holder), but my father is the policyholder (just with a different holder).The SF classes are as follows: Liability SF 13Complete SF 20 Now I have my driver’s license since 01.10.1997 (I’m 36 years old). So I have 18 years of driving license and can therefore come to SF 18 maximum? Is this correct? Do I have to pay attention to anything else? Thank you and greeting C 37 RS