if you can go and meet the dog first before deciding, that would be best. If you can't, ask the person you are getting the dog from detailed questions about bonding and personality.
I looked at a number of cavaliers before i got Zack who was 4 months old. i was looking for an older puppy, up to 6 months, but was not against an older dog if i found the right one.
I think most dogs, and cavaliers in particular, bond strongly with people, they are pack animals to their core. But like any species, they vary as to personality, that's why i would ask some specific questions.
I say this because of one experience i had, where i found a 6 month old blenheim boy from an excellent breeder, their dogs had longevity, minimal to absent MVD, all the health checks and records were done regularly, the breeder was highly recommended.
I had seen quite a few cavaliers at that point, none from a reputable breeder, so i was ready to buy that dog. They also had a 1 year old blenheim boy, same parents different litter. I was not prepared for how unfriendly both of those dogs were, especially the younger one, but neither one had much interest in people. They happily played with each other and with their toys, in a separate room much of the time. The breeder was not able to entice them to come near us, i was there for at least an hour, sitting on the floor in the living room along with the breeder and her mother. The dogs, and especially the younger, acted very nervous and avoidant of us, especially of me, but not really wanting to be near any of us; he had wildness about his behavior, very hyper, and would come around us but not near enough to touch, not wanting to be touched. I don't know if this would've changed with time in a new home, but i wasn't going to pay well over $2000 for a companion dog who was acting that way. The breeder commented on how he was acting and said something about a lack of socialization. Perhaps this was the result of growing up around other dogs and bonding with the litter mates and parents and other siblings and spending not enough time playing and bonding with people.
She said they were not keeping him because he had an undescended testicle. He was not neutered. Maybe neutering would've mellowed him?
This was just one example and was the exception. All of the other cavaliers i met were people friendly, each in their own way, each has its own personality, but i learned from that experience to not assume anything. On the phone before i met the dog, the breeder described him as affectionate, or anyway, she said he put his paws around your neck and hugged you when you picked him up. I thought he was going to be just the dog for me. He might've been perfect for someone else, a child might be good with him, jumping around and playing a lot. I was looking for something different.
Before i got one, I had gotten to know my daughter's cavalier, Belle, who was chosen because she crawled up in my daughter's lap at the breeder while the other puppy was not as interested in connecting, and Belle is that way, she loves to be held. She is independent too, she's not clingy, but she is pretty quiet and calm. She will lie on her back and whimper for joy when you come home.
Zack, by comparison, is much more active and playful, he will bring the ball to be fetched off and on all day, and is excited and intense, but not what i'd call hyper, he also likes to cuddle and snuggle, and follows me around the house, to the bathroom, to all the chores, wherever. I don't know what he does when i'm not there but when i'm home he hardly sleeps, for hours, most of the day. He may lay still for long times but with his eyes open. Belle is not like this, and i think most dogs sleep more when inactive.
The first cavalier i looked at, and seriously considered getting, was a blenheim female who was approaching 6 months old. She liked human attention, and when i stood talking to the woman who was selling her, she sat on the ground in front of us and barked at the woman, she wanted to be picked up and held. But she could be independent too. I was hesitant about getting a dog who would demand attention by barking. I live in an apartment. But she was sociable, that's for sure. I guess that is a question i would ask, is he sociable, what kind of typical behaviors does he have in relation to people, what are his likes and dislikes, what's his personality like, compared to other dogs, does he bark much, has he been trained or socialized at all, has he spent more of his time with other dogs or with people. but i definitely agree with others who have said that older dogs can bond powerfully with a family, and have big advantages over a puppy in terms of the work involved, the amount of continuous attention needed, and sturdiness as a playmate for kids. I wanted an older puppy because i have a full time job outside the home and the older the dog, the better they are able to cope with being alone for periods of time.