I think the concept of "retirement" needs to be considered separately from "state pension age". The latter does not designate a retirement age, it's merely the age at which a person is eligible to claim the state pension.
The problem with saving for retirement is that none of us knows how long we will live, so it's impossible to know how much savings we will need.
Would it not be better to have a greatly increased state pension, payable from a much older age, say from age 80? If that were the case, then at least people would know that they needed to be self-supporting until age 80 and then the state would take over. So it would be easier to work out when you could afford to retire if you knew that if you reach 80 the state will support you.
Of course, that system would rely on everyone saving for their retirement throughout their working lives. Auto-enrolment would have to be compulsory, larger amounts would have to be saved and, most importantly, I think there should be a certain amount of guarantee of return, underwritten by the government.
The great difficulty with implementation of such a scheme is that we currently have a kind of ponzi scheme, with workers paying national insurance for other people's pensions and not their own. Somehow, that will have to change, though I can't think how.