Hi Steve:
I think you are just confused on ages, if it was a while back when you had your last dog.
Two months would be the minimum -- indeed even the difference between homing at seven weeks, which some people will do, and eight weeks, can mean the difference between a poorly socialised, problem puppy that doesn't have much self control (learned from mom and siblings), to a puppy that is on its way to be being a well adjusted dog. The mother gives a lot of behavioural guidance to a puppy between 5-8 weeks in particular and thus taking on a puppy earlier than 8 weeks is risky (and no responsible breeder would consider homing a puppy before then anyway).
I'm quite sure you wouldn't have had a puppy at four weeks -- at that age, they are usually still feeding off the mother and only just learning to eat solid food -- a month old puppy on its own would be an emergency rescue case!
Cavaliers bond so well with people and respond so well to positive, rewards based training that a few weeks either way in age (over 8 weeks up to 12 weeks) is not going to make much difference in how the dog bonds to you or its willingness to learn. Indeed most reputable breeders generally will not consider homing cavaliers until between 10-12 weeks as they are so small -- AND because it is actually EASIER to housetrain them once they are slightly bigger and easier for most people to manage a slightly older puppy. They are so small as puppies that they can easily squat and go in carpets etc without anyone seeing and every mistake like that is a step back in housetraining. Those few weeks extra over 8 weeks with the breeder mean you don't need to be taking the puppy out every single hour as you will need to with an 8 wk old. It is a much, much easier task with a 10-12 week pup. Also a good breeder will have helped the puppy start to learn housetraining, not teach it poor habits! So that will get you off to a good start. Any breeder who isn;t starting the puppy off with housetraining in a very positive and beneficial way for the new owner would be questionable, too.
Be sure to research breeders very, very carefully. There are health issues that can affect lifespan and quality of life in the breed and a good breeder's breeding programme will be designed to work for longevity and good health. There are lots of links in the Library section of this site with advice on finding a good breeder. For me, a breeder willing to home before 8 weeks would raise red flags.