The bottom line is that new law has been enacted. It’s a persons right to decide when they retire. That decision will be subject to an ability to pass the checks and personal circumstance.
The key word in all this is ability. Just because it delays an F/Os promotion by 5yrs or so is no reason to discriminate against age.
The F/O when he/she does get command will probably need to work until there’re in their 70’s by then anyway, especially in light of the governments track record on savaging personal pensions when they get short of cash to squander. Try getting to the end of a long hard working life, to discover you can’t afford to live on what’s left of your pension without the years left to make up the loss.