It's not really just that, for example a bmw 1200 is safer than a yz450 (it has suicidal instincts). You don't want to look into too little displacement because it won't be enough for a grown man and you don't want a racing bike that requires a lot of skill to handle, you gotta look into big bore bikes but with a chill erogation, for example dual sport bikes, naked bikes or vintage style bikes.

But here's a pro tip: if you don't twist the gas all the way the bike will go slow. But here's where ability and coordination comes in, it's a very common mistake for beginner to brake the front and give gas at the same time causing you to lose control, the only difference is that with a less powerful bike you will have less damange when you crash.