Often it is easier to get forgiveness than it is to get permission. A 14 year old should be able to bike a fair distance without permission, assuming no unusual risks. That is in America; in Croatia I haven't a clue what the customs and dangers are and cannot advise. Presumably your parents are looking out for your interests. Unless you believe they are not, the best course is to trust their judgement.

I want to go to town to exchange 20 euros to Croatian money so I can go to a store and buy something. I would like to go in the morning since my parents are at work and I have time. It's 13 minutes to exchange, 3 minutes to the store, and 12 minutes back. That's nearly 30 minutes of my life I went to town alone. BTW: I'm 14 and I have passed my bike license.