That's a weird article - so Ofcom are investigating them because they were checking users were over 20, but had said somewhere they were checking you were over 23. Given you only have to be over 18 to partake in the deep spiritual debates that I assume take place on OnlyFans where exactly is the issue Ofcom are investigating. "your being investigated for not breaking the law" ?! I wonder if they feel there need to be a few news worth pieces to show that the regulator "has teeth" so to speak?
FWIW generally the age estimation stuff I've seen seems to set the threshold at 25, ie under 25 in the eyes of the AI and you "fail".
I did look at Yoti as a solution, but they were a few hundred a month for something like 900-1000 check a month. One other I've just finished chatting with was agechecked.com. Their plans are more of an option for a reasonably busy site. With checks ranging from 30-40p each, but with a minimum of 100 checks per month (you essentially make up any shortfall). Waiting to hear back from one other, but they have already said they are an "enterprise" solution so are looking for clients doing 1000+ checks a month so I doubt their pricing will be affordable for the amateur. I have registered with Stripe now (which is a bit of an understandable faff since it's 'finance' and you need to tell them your life story), so I'll find a little time to test their solution at some point.