Well, the age does not matter. You need to get them to the correct weight to be able to breed. A female needs to at least get to 1500 grams. Though, if you bred a small female (maybe a 2 year old snake) that weighed 1500g you wouldn't get many eggs.
If you bred a Spider x Pastel you would most likely get Pastels, Spiders, and Bumblebees.
Age DOES matter. It's recommended to breed a female in her 3rd winter, and about 500 grams per foot in length. Although some younger females may go - if they aren't mature, they are less likely to.