More snake ignorance but not your fault. The wives tales surrounding reptiles are numerous.
Simply a supposition with made up numbers to illustrate a point:
If the LD50 of rattlesnake venom is 25mg and actual venom is 10mg/ml, and if a neonate's venom load is only 2ml, then it is not able to deliver a lethal dose. If an adult rattlesnake has a venom load of 5ml, then a bite from an adult has more potential to deliver a lethal dose.
Additionally, the longer fangs of adults mean a deeper delivery which is significant in the delivery of any substance into the human body.
Bite sites are also significant in the outcome of envenomations.
Having said this, it is true that as much as 50% of bites from North American vipers are non-envenomations or "dry bites". Last I heard it was something like 3-5 fatalities in the US from snakebite. Most venomous snakes in the US are very unlikely to kill a human. Anti-venin available now is wickedly effective treating snakebite.
The case of juvenile rattlesnakes "not knowing how to control their venom" is next to ridiculous.
I have been out of the research world for quite some time but last theory related to this was that adults don't waste venom on non-prey items and juveniles just bite and deliver due to their tenacity to survive.
So there could be a smidgeon of truth to this.
Another positive for most BA people is that there is only one venomous snake in Northern California, the Norther Pacific rattlesnake, Crotalus viridis oreganus. It is not considered t be a particularly toxic snake as far as California rattlesnakes go. They don't get too big either. Its SoCal brother, the Southern Pacific, C.v. helleri is a whole different matter. That one is very nasty. Small but nasty.
I understand why you killed the snakes. Concern for your family and dogs make sense for it.
I would challenge you to try an alternative Mr.Green. See if there is a rescue organization within your area. Keep a hoe and a bucket handy and use the hoe to simply scoop up the snake and deposit it in the bucket until the snake guy comes to get it.
I volunteered my time and $$ with the Sonoma County Reptile Rescue for many years. I collected dozens (probably more) of rattlesnakes and non-venomous snakes from good folks who took the time to secure the critters and call us.
It was funny that pretty much all of the calls I went to were either educated or wealthy people.
Like or hate snakes, they have a very important place in our ecosystem.