It is never too late.  However, in your 30s you might have more obligations than you did earlier in life.  If you have a family and/or mortgage, etc. these will limit your options.

There have been many people who have changed careers late in life, people becoming doctors, authors, musicians, teachers, etc. 

If your dream is to make a change, sit down and come up with a realistic plan.  Be honest with creating the plan so that you do not give up.  It will take work and perseverance, but most people that I know that have switched careers have been ultimately much happier.