It really depends on your experience, the services you are offering ("English lessons" is really broad...are you doing exam preparation, interview prep, preparing oppositions,...working from a book, providing your own materials? etc.) and whether or not you are working legally.

Most people who are charging 25€+ per hour are native English speakers who are legally registered freelance English teachers.

Generally speaking the average rate for English teachers is hovering around 15€ per hour. This is the standard rate for those working under the table (i.e. illegally) and/or don't have much experience. However, I have seen rates as low as 9-10€ per hour.

Some people work out their rates depending on if they travel to their clients or if their clients travel to them...and also the kind of cancellation policy they offer.

Just some things for you to keep in mind.