I started ballet when I was 2 and we did a gradual progression up to pirouettes. First we did exercises getting from fifth to pirouette position, then from fourth, all without turning and on flat foot and holding the position for 4 beats. Then we did the same but to pirouette position on demi-pointe. Then we did quarter turns from fifth and fourth. Then half turns from fifth and fourth. Then full turns from fifth and fourth. Then full turns from second. Then one and a half, then doubles, then two and a half, then triples. Then singles and doubles on three-quarter pointe. Then singles and doubles on pointe holding at the end for 4 beats. Then triples and fouettes on pointe. Then multiples (more than 3) and pirouettes ending in funny positions, such as attitude and arabesque.
I started doing the first exercises (no turns and on flat foot) when I was about 6. I did singles and doubles when I was 10, although I always found doubles and triples easier (both on demi, three quarter and full pointe) than singles because you put so little energy into a single, especially on pointe. I dislocated my knee and did something to the ligaments in my ankle when I was 11 after a jumping triple went wrong and I landed on my bum with my working leg twisted up underneath me. I still wouldn't say that I can do a perfect pirouette 100% of the time because that's impossible and anyone who thinks that their pirouettes are perfect just haven't found something else to improve. My technique has always been very strong but I could spot faster and put more ebb and flow into my pirouettes.