A whole life tariff is rare there are currently 61 prisoners on 'Whole Life Tariffs in the UK. List here
https://en.wikipedia.org/wiki/List_of_prisoners_with_whole-life_tariffs
The 23 years is the tariff for this criminal, but is does not mean he will be out in 23 years. (how many times do I have to post this?)
23 years is the minimum time before he can begin the process of applying for parole. It is VERY unlikely he will be granted leave to apply for parole at the first attempt. In any case it takes several years for even a first application to be heard. A more realistic date for leave to apply for parole would be 30 years , then a few more years after that if it is granted before release 'on licence'
Life really does mean life, a 'lifer' can never be freed only released 'on licence' The life sentence remains in place for the entire life of the offender, one mistake arrest or breach of the licence conditions can see the offender back in prison without another trial.