Old medical student going into IB. How screwed am I?

So, I am a medical student in Brazil in a top-ten medical school here. I'm am currently 23 years old, close to graduating, but only finished my major due to family pressure. Dislike medicine. Actually planning on going to top business school around here in Sao Paulo, and getting a job in IB. Thing is, I'm pretty old. I'm graduate at what? 27 years old? That's about the average age for a first or second-year associate, right?

So, suppose I was a guy from a target school with 3.9 GPA in the US. How much would I be harmed in the interviews due to the fact that I'm a 27 year old dude looking to get into an analyst position?

I'm asking this at a massively London/NYC-focused forum because I imagine the culture should be far more competitive and unforgiving with any minor deviances - like older age - than in Sao Paulo. It's a good benchmark, so, let's be pessimistic.