he has a girlfriend and if he has she is 18 years old?

i think she was 18, ive heard rumors on ファンポップ saying it :]

i don't know how old she is but i googled it because i've read that he 発言しました it to Finnish magazine, channel または newspaper and i found it ! あなた can look at it and if you're not Finnish use Google translate =)
link

and i have heard that she is from Finland!
go Finland!

こんにちは あなた guys!
This Nora must be a nice girl, otherwise Alex wouldn't fall for her!
I'm just happy for him if it works out!
If Alex happy, I'm happy! <3

No, his special girl is from Norway, not Finland.

mtv3's article's translation with Google translator;
Norwegian Eurovision Song Contest winner Alexander Rybak, 23, is a happy man, because half of the hand is now a new love.

Success and record sales in spite of Alexander lives in Oslo neliöisessä a modest 20-room 71-year-old lady's subtenant. Dream on final outcome, however, also purchase their own homes.

- Previously, I was 空想 in good condition poikamiesboksista, a Playboy-style mansion makeilusta, but now my mind has changed. I'm in 愛 and I would like an idyllic family house far from the bustle of everything, violin urchin tells Entertainment news.

Norwegian gentleman does not want to reveal too much girlfriend, but says he is absolutely serious about respect.

- With him I could imagine to spend my life in the end. I do not want to spoil this story laver looking at all of our relationship, but I'm very happy, smiling man says.