Must.... not.... cut loose.... on..... the.... Newbie.....
As mentioned earlier - Absolute bollocks.
Having a bike, especially when you're a younger rider (not that I'm old) is about having freedom, independence, being able to get to faraway places, having a fun project and exciting things to do, things and skills to learn about, something to care for and about being a real adult. This last one is kinda taken care of when you realise how fecking dangerous it can be on those roads!!
I had a 125 Dragstar, weighing in at just 12BHP lugging 144kg. I could still outride bigger sports bikes through town. It ain't about speed and it ain't about luck either - It's always, always, always about skill.
Many people DO still buy 125s, just to play around on... and by 'play around', I mean a lightweight thing that you can throw into corners and do a bit of spirited riding on.
See above ramble about 125 enthusiasts.
In short - Ride your own ride.
If blokie wants to go blasting off like a Hoolie, fucking let him.
He'll wear out his tyres and other parts far faster and will likely end up buried in a hedge/bus/building.
Use your 125 time to learn the mental skills - Anticipation, forward planning, actually seeing your environment, timing your manoeuvres and so on. When you come to hop on a bigger bike, it will be SO much easier and there'll be SO much more you're able to do on it!!