Fix up docs/comments related to maxAge.

[dlongley]

I don't plan on doing a release with this since it's just docs, so no new changelog entry.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.10%. Comparing base (9ac3d52) to head (5325a4f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #16   +/-   ##
=======================================
  Coverage   89.10%   89.10%           
=======================================
  Files           2        2           
  Lines         101      101           
=======================================
  Hits           90       90           
  Misses         11       11           

Files with missing lines	Coverage Δ
lib/LruCache.js	88.65% <100.00%> (ø)

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9ac3d52...5325a4f. Read the comment docs.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.