The three teenagers never described the suspect as 25-30 years - only the October 13th 1969 police sketch did. Their account was comprehensively detailed in the police report countersigned by Officer Armond Pelissetti on October 12th 1969. Their viewing of the suspect "last seen walking north on Cherry Street, from Washington Street" was the only eyewitness testimony in the police report, and therefore the suspect description on page 2 could only have been derived from them. It stated the man was in his early forties. It couldn't have been from the other two sets of eyewitnesses because the police report clearly states that the suspect was "last seen walking north on Cherry Street, from Washington Street". The other eyewitnesses viewed the suspect after Cherry Street.
The three teenagers sat down with a sketch artist who interpreted their description of the man - and it's extremely likely that because the sketch was interpreted and drawn looking younger, the police attributed the age range of 25-30 years to it - likely believing this was the correct course of action based on the appearance of the sketch. In other words, the contradiction of the three teenagers early forties description in the police report to the appearance of the sketch, likely played a part in the revision of the age range placed on the wanted poster. However, it is apparent that the three teenagers were not happy with the first sketch, forcing the police to create an amended sketch more in line with their original early forties description. The police then released the amended sketch on October 18th 1969 with a compromise age range of 35-45 years, which allowed for any slight error either way.
Here is an excerpt by Donn Devine: "But just how long is a generation? Don’t we all know as a matter of common knowledge that it generally averages about 25 years from the birth of a parent to the birth of a child, even though it varies case by case? And wasn’t it closer to 20 years in earlier times when humans mated younger and life expectancies were shorter? Where did those numbers come from? Several recent studies by a sociologist-demographer and groups of population geneticists and biological anthropologists show that male-line generations, from father to son, are always longer on average than female-line generations, from mother to daughter. They show, too, that both are longer than the 25-year interval that conventional wisdom has assigned to a generation. The male generation is at least a third longer, the female generation is longer by perhaps half that amount".
Most people affix around 20-25 years to a generation, so if we took the average of the four victim's ages from the first two attacks, we would arrive at 19 years. Add the generational divide of 20-25 years and we have a suspect between 39-44 years of age - a man in his early forties or about 40. We know the attack at Presidio Heights was a Zodiac crime because of the blooded piece of taxicab driver Paul Stine's shirt being mailed to the San Francisco Chronicle, therefore these three sets of eyewitnesses, in a time window of just five minutes, all describing a man about 40 years of age should carry great value. But does this argument have any sway with the long-held convictions of people regarding suspects in the Zodiac case, or will no amount of eyewitness testimony cloud the lens through which they view the Zodiac case?
In 1969, the ages of the most widely touted suspects were: Theodore Kaczynski (27), Bruce Davis (27), Gareth Penn (28), Ross Sullivan (28), Richard Gaikowski (33), Arthur Leigh Allen (35), Richard Marshall (41), Lawrence Kane (45) and Kjell Qvale (50). Based on the eyewitness testimony at Presidio Heights, only two candidates fit the age description of the Zodiac Killer and these are poor suspects at best. The farther we travel to either end of the suspect age-scale spectrum, the weaker the argument becomes for these men to be the infamous Zodiac Killer. People often defy their years, but the argument still stands.
We have multiple eyewitnesses at Presidio Heights, all of whom were able to give fairly detailed descriptions of a killer emerging from the taxicab, heading up Cherry Street, turning into Jackson Street, before seeking refuge in the Presidio Park just after 10:00 pm. The question is, what faith do you have in three corroborating sets of eyewitnesses?