In my opinion it depends.
Generally I think it's appropriate gift of small sums (50-100€) to teenagers and students, so they can buy themselves what they prefer - that's what I did with my brother and my wife's cousin.
I'm "just" 26, but I admit I have no idea what things teenagers like my brother or wife's cousins are into, so monetary gifts are the best choice so I know they will be getting something they like or that they need.