If you want to be sure that well-behaved verified bots like GoogleBot can bypass your age gate you will need to create a Cloudflare HTTP Request Header Transform Rule for the plugin to detect. You can do this with any Cloudflare account, including the free plan.
Navigate to your domain name. On the left menu look for Rules -> Overview. In the right pane a list of all of the rules configured for your domain will appear. Look for the Request Header Transform Rules section and click the Create Rule link.
When you are on the Create new HTTP Request Header Transform Rule page you will need to click the Edit Expression link. (The cf.client.bot value is not available in the Expression Builder mode presets.)
Give the rule a descriptive name. Select the Custom filter expression radio if it is not already selected. In the expression editor enter (cf.client.bot). Then you need to set a dynamic header named "verified-bot" with a value of "cf.client.bot".
If you add it as the first transform rule it will ensure no other rules bypass setting this header.
The transform rule you are creating should look like this.
