125cc or more? (maintenance costs)

Hello! I will be 18 in a few months and have been driving a 50cc scooter for 5,000 kilometers. Have my car driver’s license in my pocket and let myself be persuaded above all by relatives to leave the motorcycle driver’s license away. I itch the motorcycle riding extremely and envy every biker who overtakes me and my scooter on a beautiful summer day. My first question to you would be, is worth with just under 18 still the A1 driver’s license? My driving instructor has said that the price of the A2 will only be but he said that the A1 is much easier (why?). Suppose I make the A2, then I want a bigger bike of course! Since I really like the super athletes like Yamaha YZF and am only about 1.70 big, my selection is limited (Can I forget about Enduros with my size?). The A1 machines cost hardly more in maintenance than my scooter but what does it look like with a bigger one? Suppose 300-600cm with 30-40 hp? Apart from that, wants to If I get a bigger one than a 125cc? At the Yamaha YZF R125 I only touch the ground with the football. (seat height approx. 83cm) Is this an obstacle? This is also the case with my scooter, but I always put one foot on the footboard and put the weight slightly on the other side around the ground completely. Is this also possible with a motorcycle? Would I be very pleased with your answers! LG Baye rnRider