Update cache-responses.mdx (#21156)

Age headers do not appear on Lower Tier HIT that are served from the upper tier cache

Author: seaneustace

src/content/docs/cache/concepts/cache-responses.mdx

@@ -12,7 +12,7 @@ The `CF-Cache-Status` header output indicates whether a resource is cached or no
 :::note[`Age` response header]
 The `Age` response header is a header returned from cache that specifies the time in seconds that an asset has been in Cloudflare's cache. This value resets if the asset is revalidated, purged, or evicted and then re-cached.
 
-The `Age` header is only present for responses served from the cache. It will not appear on a cache MISS, dynamic traffic, or any responses that did not originate from the cache (for example, responses generated by a Worker that bypassed the cache).
+The `Age` header is only present for responses served from the cache. It will not appear on a cache MISS, dynamic traffic, the first request that populates the lower tier HIT from tiered cache `CacheTieredFill=true` or any responses that did not originate from the cache (for example, responses generated by a Worker that bypassed the cache).
 :::
 
 Below you can find a comprehensive breakdown of Cloudflare's cache response statuses.