If you wear hearing aids you can get a Disabled Persons rail card for £20. It also entitles the person travelling with you to the same discount. There is no minimum ages for this card
https://www.disabledpersons-railcard.co.uk/using-your-railcard/the-benefits/
I wish I'd known that before.
My partner wears hearing aids. As we seldom travel by train we've never bothered to get a rail card but this would have saved us money on just the single recent journey to Gatwick.