Is 27 Too Old To Learn Guitar?

I actually agree with alteredmind, it will eventually piss you off. There are always these moments when you think you are getting pretty good and all of a sudden you start making mistakes and fuck-ups. It's totally normal, you don't have to practice with a smile on your face all the time, regardless of being passionate about music or not.
 
It could be argueable that 'back then' was a better time, what with all the baby mozart stuff now, but screw it, there is no better time to learn an instrument.