Sarveshaam aadhi bhootatvaath puraatanaa
Puraatanaa means ancient. Divine mother is the beginning of everything. Creation came from the attribute less Parabrahma. All the worlds came out of it. Because it is present even before the first ever thing that is created, it is being referred to as the most ancient one.
Hayanaatmaa mahaadevah prajaapathir iti smrutah
Tantras say that Prajaapathi is the personification of Kaala (passage of time). Only Parabrahma does not change in time. At the beginning of creation, Time also emerged (along with 5 elements) from Divine Mother. At the end of creation, it will dissolve into her. We learnt this in the name Kaala hanthri. She neither has a beginning nor an end. She is eternal. So she is the oldest of all. Hence she is being referred to as ancient.
Vishwam vishnurvashatkaaro bhoota bhavya bhavatprabhuh
Bhootakridh bhootabrith bhaavo bhootaatmaa bhoota bhaavanah