I've seen the record of one chap who married in 1861 and his age was given as 21. He died in 1896 and his age was given as 80. Meaning he managed to age 59 years in 35 years!
I've seen adult siblings recorded with the wrong ages on census records whereas you would think they should know the order they were born in.
I've seen records of the same people going by multiple surname spellings such as O'Neil/Neil/Neal, McMullan/Mullan, Lees/Leese/Lee even into the early 20th century!
In comparison, Scottish records are much more reliable and spellings and ages are correct in the far majority of cases in civil registration records.
So how come the huge discrepancies in Irish records?
I suppose it could also be to do with the Irish officials being less strict in their record keeping.
My Irish great-aunts and uncle aged 2 decades between 1901 & 1911 census. Eldest great-aunt outlived all her immediate family and died 30 years later, aged only 15 years older on her death certificate than on 1911 census. Great-Grandma, their mother, was officially 70 on 1901 census but since she'd been married 60 years by then, the age was underestimated. Her husband's recorded age at death was 88, meaning, if accurate, he may have been born c.1810. I estimate that he was between 80 and 100 when he died.
There were no set spellings of names in 19thC. If a person could write, they spelled their names however they liked. Members of the same family might spell their surname differently. An example of this is a man who informed the registrar of his brother's death. He spelled the surname one way for his brother's name and a different way for his own. When registrar queried the 2 spellings, the man said his brother used a different spelling. People who couldn't write had no control over how their name was written.
Consider that provision of elementary education in Ireland was later than Scotland.
Consider also that English was not the first language for some Irish people.
"O" and "Mc" prefixes might be adopted or dropped, depending on a variety of factors e.g. to seem more or less Irish.
Civil registration for everyone began in Ireland a decade later than Scotland and 3 decades later than England.