Re: At the risk of being branded misogynst...
@Peter Gathercole your assumption that higher pay should come with time served is nonsense. EQUAL PAY FOR EQUAL WORK. Age discrimination is just as bad as sex discrimination or gender discrimination or even racial discrimination.
As you say, it's a fast moving industry. As a result, the required skills are the ability to update skills, not the skills themselves. This means I could miss a year and still be better than colleagues who aren't as good at upskilling. I've also seen 22 year olds who run circles around 45 year olds - this is in fact becoming more common given the rapid change in skill-sets and a reluctance to move with the times. The phrase "I've been doing this for 20 years!" isn't usually a good thing any more, especially in IT. It's not specifically bad, but if the thing you're doing is server installs and you've not learned cloud then it's certainly not good.
You're also assuming that she would need to "relearn". Also nonsense as any woman in a sufficiently senior position for this to matter would likely keep themselves up to date throughout maternity leave. I manage it while on holiday so I'm quite certain the girls can do it too for as long as needed.
Why do you think the climb to the board takes 20-30 years? Tech in particular has extremely young exec level staff. Bill gates certainly hadn't been at it 30 years when he became CEO of Microsoft!