Do cat's personalities ever mellow?

[ProperLavs]

In April I got 2 kittens, brother and sister. The girl was ultra chilled out and hr brother the polar opposite. One day a couple of months ago the girl simply didn't come home.
Now we have just the boy- now 9 months who is supremely aloof and a Neighbourhood terror, always scrapping with next door's bigger Tom.
We currently have a live mouse in the sitting room, yet another present.
The boy doesn't like being picked up, doesn't do laps and will allow himself to be stroked for about a minute a day.
I am assuming he going through the terrible teens?
Will he ever become a more chilled out puss?
We love him dearly but do miss his chilled out sister a lot still.
I would love to get another kitten but am scared he would beat it up. He beats up next door's dog so the owners tell me

Alot depends on the envioment they are living in.

Your cat is neutered, right?
Mine became lapcats recently, which is quite a big chill out.

Dboycat is still chilling out. He is around 4 now, was neutered at about 1yr. He is still wary and scared, but will increasingly come and sit on laps and ask to be stroked. He doesn't follow us around like dgirlcat does but she will lash out if cross whereas he is very gentle. Is he neutered?

Yes, he was neutered in July. he is just such a feisty little sod. He was always less affectionate and much more nervous even when very small. He will follow me round the house when I am doing housework.
We play with him loads to try and help him burn off energy and he is great fun to play with.

Some cats are just like that, I'm afraid. They do mellow with age. My old girl was quite affectionate by about 10 or 17.