Tricep strength will vary from individual to individual based on insertion points, bone length, etc, etc, and I doubt if you will find a ratio of tricep strength to bodyweight. Just to satisfy your curiosity though, I never do direct tricep work, but do P bar dips all the time. Age 55, WT approx 180, HT 5'8" just did 13 P Bar dips with 65 lbs strapped on. No great shakes.
Personally, just concentrate on basic compoud moves, build up some strength at the same time as you "tone". The definition of "one" at this site is just building some muscle and losing the flab around it. Beginner's can usually do this simultaneously with little problem. After that it gets a little tricky. But anyway, just pick good solid pressing movements and your tricep strength will rise rapidly without getting into all thos tricp pushdowns, etc.