Lots of great thoughts on here, I'll add my few.
Timing - some people have it from the start but it most certainly can be learned. The people that are blessed with it and learn and add to their natural ability will be your champions.
Timing for a person that is the attacker (to me) is seeing a weakness in what the opponent is doing at the time (maybe they have their feet in a position where they can not react as quickly as normal) and being able to quickly "React" to what they see and land a kick or punch which they initiate as the attacker. I'm a counter puncher by nature but even when I am the aggressor my attack usually comes from when I saw an opening of some sort. Timing and reaction go hand and hand together to me.
Timing from the counter puncher point of view (whether you were 'born with' or 'learned from experience') is the reaction to a punch or kick thrown, the ability to react to this with your own counter. Nothing magical here. I'm a counter puncher by nature.
Quick story, When Steven's Segals "Above The Law' movie came out the opening scene when he is in his dojo caught my eye. I watched those scenes on my VCR, slowmo, pic by pic, to find out what he was doing. All counter strikes, and this became my signature move for years. (Fun Fact)
Timing against another person can absolutely be learned. Many people give away their attack prior to even throwing it with some type of move with their body whether it's a quick short step prior to a kick or some type of hand/arm movement prior to initiating any type of punches etc. You just have to pay attention and know there are things to look for.
Big high flying kicks - love to watch them in tournaments but unless you are wearing your Chuck Norris Action Jeans they probably aren't that useful on the street, unless you walk around in your gi (please don't do this) . Some of you guys remember those jeans

. We used to allow leg whips at my school but too many people were getting hurt so we went back to above the waste (except for sweeps of course)
SIZE - I haven't seen any mention of a person'ssize but it definitely matters.
Age Matters - My skills and tricks still enable me to hold my own with my 20 year old students (I'm 61) for a short while, but someone mentioned Stamina before and they are right, I need to end something quickly or I need to get to the car and drive away.