Where to begin CM with multiple ages

Here’s a helpful series if you’d like to have family style learning by combining homeschool grade levels.

http://simplycharlottemason.com/series/combining-homeschool-grade-levels/

You may find that you can only combine a few subjects with such an age span.  If so, you might want to have family Bible study, picture and composer study, and nature study together.  Then, your highschooler can follow a more independent CM study routine (use SCM guides and resources mostly on their own, CMH syllabi, or AO come to mind.)  This would allow you time to spend with your younger child in order to solidify reading and math skills, habits, etc.

That’s probably not the quick answer you thought you’d receive, but it depends on what you have in mind.  If subjects are studied together, the SCM guides are excellent!  Family read alouds from spine books keep you on the “same page” in history/geography/Bible.  Then, just use the chart for your highschooler to add in titles that cover the time period.  You may want to have a family timeline, or your highschooler can complete one independently.

Math, of course, will be studied individually.

You might want to have another family read aloud going for science, have your highschooler study a science topic independently, and enjoy some early level science topic books from the library with your kindergartener.

For years, we’ve studied most subjects together.  Our last two children are 6 /12 years apart.  The 14yo is ready for some topics that are either not a good fit for our 7yo, or aren’t necessary (IMO) for her at this time.  So, this next year, they will have fairly different studies. 

Independent, everything together, or a combination of the two are all good ways to learn in a CM style.