I'm just a guy but have recently gotten into running again, ran a marathon about a decade ago, and got fit for new shoes last week (New Balance 1080s).

Conventional wisdom is running shoes will last about 300-500 miles but this is not a concrete rule. The insoles will form to your feet and lose springiness and support. The soles will wear down reducing traction and lose support.

I tend to wear down the topsides around the outside forefoot and big toe area and the materials starts to tear.

It's not really a problem, per se, to run in old shoes but the experience will likely be better with new ones. Technology and materials get better, lighter.

I think a proper fit matters more than new/old. My oldest pair of shoes I still wear are from 2006 (Birkenstock Boston)

Good luck, running is high impact and best to run on trails/dirt/grass when ramping up again rather than pavement.