sesha 118...how?

both shivanya and sesha were kids in the flashbacks they showed in naagin1 then how sesha is 118?
n sesha was also daughter of naagin right who was shivanya's mother's sister but got thrown away from naag world...😕

This is my theory, so the mom and dad of Shivanya's and Shesha's mom gave birth to many kids like more than 100 like adam and eve but all kids looked of same age bcoz they were Naagin, Shesha's mom must be around 80 years older than Shivanya's mom but they looked of same age bcoz Naagins age very slowly...Same is the case with Shivanya and Shesha, Shesha is 118 but Shivanya is around 50 but looked of same age in season 1 bcoz they were naagins...Now Shivanya has aged bcoz she's a human now but Shesha has'nt bcoz she's a naagin...Shesha was a born naagin and did'nt did any tapasya for 100 years.