Displacement is just a number. The style of motor is what makes a difference. While my girlfriend’s s40 may have a displacement of 652cc maying it larger than my 600cc FZ6R, they are DRASTICALLY different. Her machine is running a single cylinder “Thumper” putting out 31HP and 33.6 FT.LB of torque making peak power at 5,200 rpm, while my smaller inline 4 cylinder puts out 78hp and 44.2 ft.lbs of torque making peak power at 10,000 rpm. Big difference?
Think about the GSX-R600 that a ton of new riders on this site think is ok to start on. It may only have a 599cc displacement, but it’s inline 4 churns out about 109hp, and has a top speed of about 160mph!!!!!! Only slightly slower than the top speed of a Shelby GT500 (with the governer removed, otherwise the GSX is faster) or a Challenger SRT-8 (top speed of 170mph) However, it would beat both in a 1/4 drag with a time of around 11 seconds for the Suzuki, 12.5 for the Shelby, and the Challenger in last at 13.8. Still sound like something that screams beginner?
So don’t focus on displacement as a means of determining whether or not a bike is too much for you as it is a poor indicator. Look at the output of what that motor can do rather than how much space it takes up.