In a perfect world, the 1500 grams for a female and 600 grams for a male formula works ... but ....
Young males can many times be lousy breeders ... with an aggressive feeding schedule, sure you can sometimes get a male to 600 grams in less than 12 months ... then when you put him with your girls he just cowers in the corner ... it's because he's still a baby ... other times those young males will get in there an tear things up, but you might not have a whole lot of success getting eggs ... and then sometimes young males do just as well as older males, but that is very very rare ... it all depends ... One thing for sure is that older males in at least their second or third winter above 750 grams will do a much better job at breeding and fathering clutches than younger smaller males ... age definitely matters.
Females are the same way ... you can get a female to 1800 grams in 18 months, that doesn't mean shes going to lay eggs ... when breeding females in the thrid winter or older about 90% of what I breed goes on to lay eggs ... when I breed 1500+ gram females in their second winter my success rate drops to about 10%. Sure, young girls "can" do it, but not as reliably as older girls. Also, a 7 year old girl that is 4.5 feet long and 1500 grams is in NO condition to breed ... too thin.
Weight and age are all relative ... grow your snakes, make sure they're healthy and have fun ... there are no short cuts!
-adam