The protective and affectionate layers of parents upon their kids are essential conditions of healthy growth of a person. But this protective shell should be loosing by and by as the child grows. It has been a vital issue that when a child can be allowed to take their own decision. The age at which children take decision for their career initiation has really very unpredictable maturity level. No doubt parents do not trust their children which results in conflicts between parents and their teenager-children.
There is no fixed age as it depends on maturity level of a child and it differs from child to child. The factors that make a person matured are:
Influence of others opinions: Are you influenced by others opinion very easily? Being very lenient to others opinion is not good. Listening to others suggestions and respecting others views are one thing and making final decision is another. On the contradictory being over stub born is also not good.
Self Assessment: How much you know your capacity is very critical part. Everyone is blessed with some special quality and everyone is different from another. It is not necessary that if your friend is good in some field then you will be good in the same field. And copying others always spoils your own decision making capacity. Just try to find out in which field you are good. If some field fascinates you then find out the reason of your interest.
Confidence and Consistency: This is the most important factor. Your self confidence can make you successful in new and strange fields too. Besides you should be consistent with your thoughts.
Practical Thinking: Some fields require huge amount of investment and students having less financial resources that can not bear that. So being practical is also a good advice. However there are many financial aids available to help needy students. So for higher education this should not be a limiting factor as students earn from part-time jobs too.
If you qualify all of these criteria then you really deserve the freedom of choosing your own career and life style.