the vet said we should have had him fixed sooner as he is housed with his mother and 2 sister cats.
Were both vets at the same clinic?
I suppose this can happen either way - but when to get them snipped depends on a few factors.
-Where you got your kitten
-What your vet is comfortable with
-What is standard in your region
Where I am the big rescues have specially treained vets that will do early s/n - so if you get your pet from one of them it can be done as early as 6-8 weeks.
However, if you did not go to one of those particular rescue groups what age your pet can be s/n at depends on the vet you choose. We have a clinic that does mostly s/n, and they do the next earliest at 4 months.
The rescue I work with partners with vets who will s/n at 4 months and 4 lbs., kittens adopted out younger must be done by the time they're 6 months and proof sent to the rescue. The cost is included in the adoption fee if the adopter goes to specific clinics.
Most vets where I am won't do males until 5 months, and females at 6 months. Although it is slowly changing as new methods are brought in a new vets become more comfortable doing a procedure on a younger pet.
When is my baby beast gonna stop growing?
Lol, sounds like you'll have a big boy. The 6/7 months thing never seemed to be my experience. All my kitties did MOST of their growing by that time, but looked like silly skinny teenagers. They all gained muscle mass until about a year, and then had a growth spurt of about a 1/2lb at 2 years. Even tiny Torri gained 1/2lb at 2! (To make her a 'gigantic' 6.5lbs)
Maine Coons are known to grow until they're about 3 years old. They have a lot more growing to do than an average kitty, so it makes sense that it takes longer. Keep an eye on his overall condition, rather than worrying about his actual weight. And feed him like he's the growing kitten that he is!
the vet who entered him gave us a bit of a hard time about it saying he was too large to be that young
The vet was being a pain, basically.
Technically at 4 months he could possibly be old enough to mate. Some males are and some aren't. In my last litter we had one male and one female until they were 4 months, and the male was definitely starting to display more 'male' behaviors (mostly being a brat with his sister and scruffing her, then he got really confused and had no idea what to do next! XD). They went in to be neutered and then went on to another foster home.
The actual likelihood of him having enough testosterone to actually mate and impregnate a female at 4 months is pretty darn low. Not impossible, but very minimal.