How are younger objects outside our observable universe when the older CMB is an observer's temporal "edge"?
The part of the universe that we can see is a cone in spacetime (our past light cone) and there are young and old parts of the universe both inside and outside the cone.
Here's a picture from Ned Wright's cosmology tutorial that shows what's going on.

We're at the top center. The red lines are (a slice through) our past light cone. Ignore the wavy $\phi(x)$ line and imagine a straight horizontal line there instead. Below that line the universe was opaque, so our observable universe effectively ends at that line (just like our view of the sun ends at its surface). There are young and old galaxies, stars, etc. both inside and outside the cone.