Age limit for registration on Alert 13 years?

We contacted the ICO on 23 May 2018 to obtain clarification on the 13 year age limit set in the GDPR legislation. The response was as follows:-

“First of all, it’s not marketing, this is a messaging service that people sign up to, so if you put a limit on it that’s up to you. There is nothing in the legislation anywhere that says about an age unless of course we are talking about providing services to children where it’s like the internet or mobile phones or something like that. So, if you feel that the content of it would be age appropriate, then you can set your own age limit on it; they are actively giving their consent to receive that information so it’s up to you what content might be in it and whether it’s appropriate for certain age groups.”