In response to the global increasing age of the population, there is general agreement on the need to define what is meant by 'old.' Yet there is no consensus on age groups within the definition of old, which makes comparative studies of people of differing ages in advancing years impossible. Attempts to sub-categorize the 'old' also show little consensus. This article serves to open a dialogue, as an illustrative example of these inconsistencies. Specifically, the aim of this research was to examine definitions of the 'oldest old' and 'fourth age', in order to highlight such inconsistencies and the need for consistent age stratifications. The authors conducted a literature search from January 2003 to April 2015 using the six most highly-rated non-medical journals in gerontology; the search was conducted again in 2018–2019 for currency. Forty-nine articles in total were reviewed. The findings show little consensus on the age stratifications used to define the 'oldest old' and 'fourth age,' which ranged from seventy-five plus to ninety-two plus years. Dividing the 'old' population into the oldest old and/or fourth age still shows a lack of consensus, with some authors suggesting that such divisions have only served to move ageism into very old age. There are terms for ten-year cohorts, which - if universally used - will mean that comparative ageing studies are possible. This in turn will inform international and national strategy documents, policy initiatives, clinical guidelines, and service provision and design. Given the growth in the numbers of people classed as old and the time span being 'old' covers, there is a real need for consensus. Definite age groupings that define people as cohorts, with existing and agreed words — such as sexagenarians (60–69,) septuagenarians (70–79), octogenarians (80–89), etc. - will completely remove the need for the value-laden term 'old' (and all its derivatives) for this poorly-defined population.