I will give this one another try.

I would think that as one ages the person learns from life. They gain knowledge from personal experience. The judgment part of the brain needs time to fully develop. Many people are not mature enough to make wise choices before 18 years of age. Think 18 is an age that most feel that an average person has reached where they have become responsible for their own actions.

It is an age where most western countries have selected as adult. Yes some have selected younger date.

I am sure you have noticed that teens often take unnecessary risk in life. Do things that can be dangerous without thinking about the consciences of their actions. This is a good example of why they should not be able to order drugs. Taking the drugs can have a effect their life in ways that they are not prepared to handle. The teen need to have a counselor working with them on the need for such drugs.

One thing that can be said about teens is that they change their mind often, very often. Many times it is in completely different direction. What they have to have today is not what they need to have next week. The wrong choice on stopping male hormones now will affect how the person will be the rest of their life. Not something you want younger person doing by themselves or to another.

Ok, I've obviously not made my question clear enough but thank you for the answers. There's much sense in them and I agree with that ( the legal age of majority used to be 16 in Iceland not many years ago though, as you said, it is like that in some countries )

When I asked why people 18 and over would need to age before getting these chemicals, I meant that some people come here and ask where they can order these hormones online, but why don't they consult a doctor?

Many doctors are unwilling to prescribe such medications, seeing a patient's desire for castration as more a psychological issue than a physical one.

Basically, many (most) doctors seem to believe that anyone who would want to be castrated must be mentally ill, and would be better of seeing a pshrink.

And they rather want the person to order the chemicals online? And about that, do these chemicals get through customs inspection without an issue in all european countries?

That answer would vary on each country. Every country has very different rules about importing drugs. People in the USA can order drugs somewhat easy and do not have too much problems with customs. Once in a while a package is opened and sent back to the sender.

You have to check with the rules that are for your country on importing this type of drug. We can not tell you the laws. Many countries keep changing the rules without warning. In the UK it was no problem for years and in the past month or so you can no longer import drugs.