They are not concerned about the age issue like here in America. They judge you by your heart and if you are a good person and not because you are a little older than her. When you write her send her some address labels with your address on them. This is a nice gesture on your part. Don't trust foreign post offices.
Postal workers can be dishonest and screen letters for money.
Send letters in duplicate to make sure the letter gets through and explain to her why you are sending duplicate letters. The best way to send letters is to send them Certified. It cost a little extra, but this way you know the letter will get to her. Don't use real fancy envelopes or commemorative stamps. This just draws attention to your envelope and you don't want this because of dishonest postal workers that may open your letter to look for money.