Question:
How long does the peak growth rate last?
Answer:
See When does a growth spurt occur for boys and how long does it last?
The problem is that “peak” is a moment in time. You are asking how long you grow faster than in childhood. That varies greatly between individuals. It happens during the two years that Stage 3 lasts but it can be a short spike of three months or a long drawn-out spike last a year or more.