I'm 20 but, well, I have a Jan bday so I graduated at 18.
The first one you posted for men and the London one posted are PERFECT for guys.Guys nowadays don't like to roll up the brim.It's just not in anymore.My bf has at least 4 beanies like the one you put up first and he's a year younger than myself.He says they are "styl'n", lol.The only guy I know that has one and isn't 10 years older than me owns only 1 roll up beanie.He only uses that for boxing and the gym.
I think for girls, you could try a slouchie hat.They make some that are closer to a beanie than a beret that are pretty "in" nowadays.
Hat's like this are really great because they work with almost any type of hair; long and straight, long and curly or even a short,short pixie cut.
The cloche-ish beanie you posted by Marnie McLean probably won't be as popular just cause the flower is kind of tacky.I would go with another non-felted cloche.I love her other one .You just have to make sure to make it long enough to look kind of like a visor up top to give it that 20s look.Some people made it too short and it's just not as cute.