I'm 32, 6'5", 230 lbs, and can dunk 2 handed flat footed. I'd like to think my training is somewhat effective. I know I'm tall but I seem to have maintained my athleticism while others have declined (referring to age).
My experience has taught me that leg strength is the base. Once you're past the beginner stages of lifting then add in simple plyos. I like super-setting squats with bodyweight jump squats. I like a set of 5 heavy squats followed immediately be 5 jump squats. I do 3 sets.
I also throw in other simple plyos such as lateral cone hops and single leg hops back and forth and side to side just going over a line on the ground and trying to be as fast as possible with the jumps.
My current program is 5/3/1 with power cleans done before squats. Today I did my 3/3/3 week with 220, 250, 280 lbs. I play basketball for my plyos.
The key to being explosive is increasing your strength but also taking the time to train your muscles to move fast. Lifting weights is slow. Even heavy Olympic lifts can be slow. It's recommended that you train with 60-80% of your max on Olympic movements. It's been found to be the best for improving power. Anything heavier gets too slow (including my last set of cleans today).