So, is it something like this?
Dear ICO,
I understand that under new rules, as the operator of a social media platform, I have to advise you how I check the age of my user. I have used two methods.
1. Looking in the mirror and seeing I look well over 18.
2. For around 55 years I have meticulously counted the number of birthdays I have had, that number being 60, which is more than 18. I did rely on my parents to confirm the first few.
I trust you find this meets the requirements.
toot.me.uk