Am I too old to change my career?

I'm 21 and I'm graduating next may with a bachelor's in linguistics and literature (i.e. to become an english teacher and/or ESL teacher) but I recently realized that I don't want to do this for the rest of my life! I've really fallen in love with geology, reading everything I can get my hands and watching documentaries about it. I want to become a geoscientist! Is this a feasible dream or am I too old to be changing my mind like this?