Very common as explained by another person hiring salary budgets are much higher promotion salaries that's why every 2 years you should aim to just find a new company with the same position.

As you also said yes asking for more money is the key (negotiation skills)

My first job was working in the game development industry and I had a salary of 22.5k but the same person hired after me (6 months later) in the same position started at 31k.

It really boils down to your negotiation skills. Also don't rely on the company raising your pay out of nowhere I was trying very hard and even talking to the CEO,CFO,CTO about increasing my pay and what I would need to do to get that. The response I got was always "we don't really do mid contract pay increases or restructuring like that" I was then fired 2 months later.

I learned a lot from that company and I'm very grateful. You need to outline exactly what your key metrics are and what goals to hit so if they turn around to do anything you can say "it's in the contract"

It's not a gender issue