A custodial sentence is the correct decision because, as Luckygirl says, other perpetrators may realise that, whatever age, they are not beyond the law.
Younger perpetrators could decide that they have sudden onset Alzheimers, some other disease and play the sympathy card to get a reduced, deferred or suspended sentence.
Remember Ernest Saunders - not a paedophile but a criminal who was sentenced to five years' imprisonment, but released after 10 months as he was believed to be suffering from Alzheimer's disease, which is incurable. He subsequently made a full recovery and started another business.
And another, a suspected paedophile whom I will not name, who supposedly had severe dementia and excused trial, but still managing to make decisions in the House of Lords on behalf of the rest of us.