Insurance with 20 much cheaper than with 18 (despite the same SF class)

Hello, I am now 18 and would like to insure my C Corsa on me. I made my A1 driver’s license at exactly 16 years and had since 2 years a motorcycle insured on me (to be exact 23 months). I can take over the SF class from these 2 “motorcycle years” for the car. I have already clarified that. However, I get only SF class 1, instead of 2. Why always.. Probably because instead of 24 months, the motorcycle has insured only 23 months because of sale t. Now my real question: If, for example, I choose Huk24 as 18 years old with 2 years of possession of a driver’s license (by A1 with 16) and SF-Class 1 I pay almost 200 euros more than if I choose myself as 20 years old with 2 years of possession of a driver’s license (i.e. with 18) and also SF-Class 1. (500 euros vs. almost 700 euros). I thought the age only affected the amount of contributions from 23 or 25 on? How can it be that, despite identical data besides age, such a large price difference is it?