Hello and welcome aboard don187.
It is ok to try before 4 weeks, if your soap passes the zap test in the way described by IrishLass (a moderator here) linked to in Kittish's post - this zap test method is dilute enough to be both informative and safe.
Document your observations, as it will give you invaluable information as toxikon suggests.
At one week the soap will NOT be good, it won't lather well and will feel a little harsh and it will dissolve really quickly, but it won't hurt you (if it's passed the zap test). If you keep on testing and writing your notes for each new recipe, you will get a really good feel for how your soap performs for you over time.
Castile takes a long time to cure, so even at 4 weeks it will be a very young soap. At 3 months you will notice just how much better it is, at 6 months you will notice further improvement. At at about 8 months to a year you will see why so many people adore castile. Then it will lather, it will be almost pure white and rock hard, will take forever to use up (unless you leave it sitting in water, then it will still turn into a goopy mess lol).
A couple of suggestions ... change your water to calculate by lye concentration (instead of water as a percentage of oils). You will be able to control your recipes a lot better using lye concentration, and this will also help you to understand the differences oils make to your recipes, as you progress.
A lye concentration of 30 to 33% is a comfortable one to learn soap making. 33% is nice, because it means you have roughly 2 parts water to 1 part lye, which is also easy to double-check in your head as you weigh out your ingredients. This percentage (33% lye concentration) will become even more useful to you later on in your soaping adventure, and will work for just about every recipe you can dream up!
Note: Soaping with a 50% solution dramatically
increases the time it takes to get to trace in castile. I wouldn't suggest doing that as a beginner, although it could be fun experiment later on (when you are well practiced working with lye solutions). I can tell you now it's annoyingly slow!
All the best