Hey man,
If there's one thing AI has taught me, it's do you what you feels right every moment.
Now I'm 18, and if you read the above posts you'll know that I've been completely confused about this as well, but the way to look at it is, that (Assuming you're near my age) you have your whole life ahead of you, and even if you're not, it's never too late to follow you're dream.
Say you went to study for 5-6 years in civil engineering and after that time now you have the training neccesary to do jobs and follow the career you want in this moment, OR you could do the alternative and work in a small time bar or whatever and build the money up to go travelling THEN look at training once you've found out what you want to do.
The point is it doesn't matter what path you take, aslong as you're enjoying the journey.
Aslong as you're enjoying the journey and living your purpose in THAT moment, you won't be missing out on anything, cos you're living that moment, and that's the only moment there is. The present one.
The way I see it, life is full of surprises and there will be times when you won't know what's coming next. In say 10 years, you could be working as a civil engineer and who knows you could be pretty high up in the rankings, but eventually you get to the point where your fed up because it's not bringing you the fulfillment you want anymore. So, you change career, and no matter what you go for, you have that training and experience under your belt, and that means something in almost any field.
I want to be a film actor, and again who know's I could be quite big in that career in say 5-10 years, but eventually i might want to change career cos I either want to try something new or am no longer satisfied with my job, but atleast I'll have the training and experience to go to a new career.
The point I'm trying to make is, your dream career is probably going to change somewhere down the line, that's not saying it will but it's likely to happen, e.g. you may have a wife and kids to care for so you'll need a steady income, or something like that. You're dream in the physical world will most likely change but aslong as you're following you're dream you'll always feel satisfied no matter what it is.
So yeah do what you feels right, take some risks, and give it everything you got. Least then you can look back and say (Regardless of if you reached your goal) I gave it everything I had.
Hope this helps out a bit mate, If I've said something that doesn't make sense (Which I probably have) let me know.

Rory.