Never heard of ebay using an external site to verify age.

Ebay only accept credit card.

Ask a friend with CC to buy for you.

It looks legit. According to Google "VerifyMyAge is a third-party safety technology provider used by online platforms like eBay UK, Shopify, and Toolstation to ensure customers are old enough to purchase age-restricted products like alcohol, vapes, or bladed items".

Perhaps eBay has at last listened to the protests about having to use a credit card. But not everyone will be happy with scanning personal ID to be verified.

Nucleus are the parent company of verify my age i believe.

I had to sign up may years ago and don't remember having to do anything via Nucleus it was all done with verifymy age, they have many more options than eBay offer, including the usual passport/driving license, electoral roll, age estimation via mobile video and many others, the real beauty of it is you only have to do it once but it is only available to business sellers.