Why doesn't my MacBook Pro Retina connect to 802.11n?

I've bought a 15" MacBook Pro Retina Late 2013 and so far everything works perfectly. Luckily I'm *not* experiencing the "Lose Wifi after sleep" issue. That said, I only rarely connect to high-bandwidth WiFis. I'm currently working with a colleague from his home office. He has a Netgear router capable of 802.11n and his MacBook Pro (also Retina, but not late 2013, so he doesn't have the ac card) connects using 802.11n and 2.4GHz on channel 1 without a problem. My MBP however connects on the same channel using only 802.11g which is pretty slow when we want to transfer files. The WirelessDiagnostics report shows I connected to a 5GHz 802.11n yesterday when we were at the client's office. What can I do to fix or at least diagnose the problem? Is it just Mavericks, or a driver issue with these new ac cards?