
I would find it unusual to not see any signs of inherited aggressive behaviour until after adolescence, unless by aggression you mean an assertive domineering character, which of course would not show up in full until maturity but would certainly be evident even in the nest while watching interactions with siblings., and the pup would be showing ambitious tendencies.
What breed is a GD?
Inherited behaviour can be modified and even masked by training to some extent, but as you have found the true characteristics will become apparent.
On the other hand if the characteristics are there in the first place, but no training or socialisation are given until late, it is still possible to bring those traits out.
Our case with our dog who was in Quarantine from 9 1/2 weeks of age until 9 months.
His care and socialisation until then would have been limited to what was appropriate for a 9 week old puppy.
In quarantine he had no physical contact with other canines, and he couldn't even see any until he was six months old and could peep over the wall, though he could certainly hear them, and join in with the barking!
On a daily basis he saw the kennel staff (all female) and the vet (male) on only a few occasions (vaccinations health checks). I visited 3 times a week, and the lady who he went to live with once a week.
He came out of quarantine at 9 1/2 months old and went to a show 3 days later, a very large busy Open show with benching and trade stands left over from a Group championship show the next day.
He was able to show, and by the third class had the hang of it (I had lead trained him up and down his 20 foot run), happy to be examined by both male and female strangers, and loved everyone (human, and most surprisingly for an adolescent unsocialised male pup, canine) and everything.
Now everything we are told about socialisation is that they must experience as much of everything by 16 weeks as possible, or you won't have a well balanced confident adult. Yet this shows that this boys inherited character was solid and resilient enough to come through without the ideal upbringing.
The only lasting negatives with him were that his first Car journey after quarantine was long and twisty and to this day he doesn't enjoy the car, digs his heels in when going in, and then settles in a corner with a sigh and puts up with it. Also even for an Elkhound eh is barky, not having much else better to do for 6 months.