No, Anne.
You can breed from stock younger than 3 years.
Assuming your cavalier has no SM or central canal dilation and is between the age of 1 to 3,you can mate that cavalier to an over 3 without SM and central canal dilation,or to an over 5, either with or without central canal dilation.
If your cavalier between the age of 1 - 3, has a central canal dilation,you must mate to an over 5,with or without central canal dilation.
If your cavalier has a syrinx,pre syrinx or dilated central canal of 2mm, under the age of 3,it's a Do not breed.
The major changes for breeders here is that a bitch who would have had a small syrinx at age 2.5 and could previously been mated to an over 2.5 year old dog without SM, is now a "Do not breed."
A bitch under 2.5 years with a small central canal dilation,previously a C,could have been mated to an over 2.5 year old dog, must now be mated to an over 5 with or without Central canal dilation.
Its not uncommon for Grade A bitches/dogs under the old guidelines to have a small central canal dilation. The old guidelines often reported SM and central canal dilation separately for breeders information and puppy buyers found it straightforward.
The new guidelines appears not to treat SM and CCD separately and is reported under a single SM grading ..from 0 to 2.
At least this is how I think it looks...
Sins