I can relate to this, as I too wonder what could have been if I had been forced to think about what I wanted to do with my life more in high school.
I want to encourage parents to help their kids think through this, so I will post some links below that may be helpful. If you have or know someone who will be going to college, or is in college, and they don't know what to do with their lives, please encourage them to really put some time and effort into this and make a plan.
I love the Wall Street Journal's site CareerJournal. It has some really great articles, including some interviews with people about their jobs.
Another great site is MSN's Collage Grad site.
And another good idea for all high school aged students is to look through some current job postings to get a feel for what jobs and skills employers are looking for.