7 year old laying eggs

[China8428]

I've had my beardie for 7 years now and no I'm not a breeder but I've always assumed it was female. Compared in contrast to my other beardie which is exceptionally larger (which I assume is male). Today I noticed that the one I've always thought to be female has laid eggs. Now none of the eggs are fertile but I'm just wondering why after 7 years of ownership this is now happening. I have separate tanks for all 3 of my beardies and they have never came into contact with each other. The tanks are strategically placed so they can't even see each other. I've heard of them laying eggs without a mate but it's usually at a younger age. Is there anyone who can provide some insight as to why after all this time it would happen.