As a twitch affiliate under 18 pay taxes?

Do I have to pay tax on my subs as a twitch affiliate? (as a 15 year old)

Of course, minors also have to pay taxes if they have an income.

There's no age limit. Of course you have to pay this if you have income from an activity.

And if that's only 20 30 euro a month?

Then you have to declare this income anyway. Whether you actually have to pay taxes is another matter.