---
title: Age
summary: null
url: https://www.fastly.com/documentation/reference/http/http-headers/Age
---

When a resource is fetched from a backend server, Fastly will use the `Age` header as a factor in [determining the freshness of the object](https://www.fastly.com/documentation/guides/concepts/edge-state/cache/cache-freshness/) and therefore the value of `beresp.ttl` in VCL.

For example, if a resource is served with the following response headers:

```http
Cache-Control: max-age=30
Age: 10
```

then Fastly will set `beresp.ttl` to `20` (30-10), and record the `Age` header as part of the cached object.  A request received 8 seconds later for the same resource would see a cache hit with an `obj.age` of `18` and `obj.ttl` of `12`.

## Revalidation

When a resource has passed its TTL and is therefore stale, Fastly will attempt to revalidate it if the resource includes a `Last-Modified` or `ETag` header.  If the response to a revalidation request is `304 Not Modified`, we will update the stored object's TTL, and reset the `Age` to the value included in the revalidation response, or zero if there is no `Age` header on the new response.

When [stale](https://www.fastly.com/documentation/guides/concepts/edge-state/cache/stale) content is served from cache, the value of `Age` may be greater than the value of the cached object's TTL.

## Expires-based freshness

When the TTL of a resource is determined by an `Expires` header, Fastly will initialise the cache object's `Age` to zero, regardless of the value of the `Age` header on the backend response.