How tall would a 14 year old 6'2 kid be at age 18?

It really depends, you may not grow at all, grow a few inches, or grow a ton! You might be able to figure out by knowing how tall the child's parents were when they were that age, and see how tall they were when they were 18. If you can't figure out how tall they were when they were 18, see how tall they are now. People usually stop growing at the age of 18, so that could also give you a good estimate. This also depends on the gender, as boys typically grow taller than girls.