Why is hair loss irregular with age?

I just don’t understand why the earlier someone starts balding doesn’t always mean they bald extremely quickly. Like what explains a 30 year old balding almost completely in 2 years vs a 20 year old who starts balding at 20 but takes 15 years to show significant loss?

Again, it is tied to the genetics. Each hair in a region has a finite number of hair cycles to it. when the hairs go through its limited # of anagen growth cycles (a growth cycle in men is between 2-3 years), then the hair often dies. The death may be partial in the Folliclular groups (normally say a hair follicle has 3 hairs in a group, one of two my die off) making the hair look like its is thinning from above (it is thinning) and eventually that last hair will fall out sooner than later. So for an aggressive balding pattern (Norwood Class 7 pattern) the number of three year hair cycles for all of the hair from the front to the crown might be 8 cycles (pre-programmed at birth) of 3 years (3 times 8 = 24 years old to balding). Not a good scenario.  Most Class 7 men will be bald by the time they are 26 years old. The same thing can occur in older men 30, 40 or even 50 and they may lose parts of each Follicular group of between 2-3 hairs each) and then eventually the rest falls out at its pre-programmed death. Drugs like finasteride, prolong these cycles making the hair last longer.

I hope I didn’t confuse you, but I got stimulated to give you a scientific view of the process that you are describing in different men of different ages.