I remember after taking many years of piano exercises, that my 4-5 fingers still needed some help to strengthen and control. I didn't have this special European system learning piano, but now I have a special European system, for the piano that gives this type of technique within the first six months in their beginning technique studies. What ages for 4-5 fingers exercises? When students can reach a full octave, and they have accomplished 27 Musicianship patterns (which is 3-5 levels), and some Black Key Technique designed for coordiation and strengthening their fingers (about 20-30 different patterns), then they are ready to really work with the 4-5 fingers, noting that those students do not need hours and hours of work to further their strength and control for their 4-5 fingers, because of this unique system. I only wished I have had this type of training that I give to my students when I was going up!
Prof. B. Woodruff