Since late last year, you can use old versions if you want to. [0] The provider doesn't enforce the runtime anymore. But I don't think it's the provider issue in the first place. At some point "node x.x" will be EOL and you won't get an email. You'll just stop getting maintenance patches.

[0] https://aws.amazon.com/blogs/aws/new-for-aws-lambda-use-any-...