Just bought a late 2013 rmbp. This'll be my very first experience with a Mac so I'm very excited but also nervous. I've avoided macs pretty much my entire life and like many other PC users, pretty much had a negative impression of them (expensive, inflexible, expensive proprietary parts etc.)
I guess using iPhones and iPads over the years has changed my tune on Apple, as those are generally excellent products. I'm worried about obsolescence with the rmbp tho. Especially since the config is basically fixed, and practically nonupgradable. How much usage can I expect out of the late 2013 model before things just slow down to a halt or it's no longer supported? 5 years?
Mac usually go to vintage after 5 years, yeah. As for slowing down over time, I've found that there are few things that can't be solved by wiping your hard drive, reinstalling the OS fresh and putting back docks and applications selectively. I tend to do it every few years on my machines, keeps them running like new (if a bit of an extreme reaction ).
You should get at least three or four of the next OS supported (not included 10.10), possibly more, just depends on if there are any big technology shifts that Apple would end support for.