could be judged as 'age discrimination'
It's definitely age disrimination.
But some forms of discrimination are perfectly legal.
For example we know very well that insurers can discriminate on age at the moment.
Not all discrimination is illegal.

if someone decides to challenge under Human Rights legislation
Yes but it would be fairly pointless because all the government have to do is to change the scheme to qualify it on lack of work experience and most older people will qualify out.

But you are right that it could mean there are more cases along similar lines.

I don't agree with the gender decision but I do think it great that we live in a democracy where ordinary people can challenge these type of things.