@steniom: I am now 31 years old. When I was younger I participated in the IOI (2001) and the ACM ICPC World Finals (2002, 2005) - I got medals in both (silver in IOI and bronze in ACM ICPC World Finals). I also trained many students in Romania throughout the years, which meant that I had to “keep in touch” with all the top competition problems (I solved many problems myself in order to be able to teach the students cool solutions for these problems). I participated in several contests in Romania on a continuous basis, but I (re-)started participating in international online competitions only since June 2012 (Topcoder, Codeforces, Codechef, Hackerrank). The first Codechef long contest that I participated in was OCT12, and since NOV12 the worst rank I got in any Codechef long contest that I participated in was 5 (only in July 2013).
Solving the 9 binary problems in long contests requires both experience and persistence (there were several cases in which I learnt/developed the concepts necessary for solving the hard problems during the 10-day period of the contest - i.e. I didn’t know them before the contest started). But solving the challenge problem requires a specific set of skills which is difficult to quantify. To me it’s a bit like research - I try multiple solutions and I understand what works and what doesn’t; and based on this I understand how to modify the working solutions in order to obtain better scores. However, “squeezing” the best score possible out of the challenge problem under the given constraints is quite difficult. The only other contests which are similar to the challenge problem on Codechef are Topcoder Marathon Matches, but they last for 2 weeks, which is too long for me to focus on a single problem.
As for @ACRush, I think he is 3-4 years younger than I am (he participated in IOI 2004 and got a gold medal there). I also think that he is generally better than me in handling challenge problems, and yet I am currently ranked higher than him [ but probably this won’t last for too long ]