I think EU ID should be accepted as proof of your age to lift age restrictions.
If you can enter the country, open a UK bank account, vote in local UK and European elections. You can even open your own business but it is not accepted to proof your age. This can be for some Giff Gaff customers frustrating and they can't fully use service they are paying for. I hope you support this idea folks and Giff Gaff will consider EU Id's as a solution. Thanks