The Attorney General decided not to refer Rolf Harris' sentence to the Court of Appeal because there were several reasons the original sentence would not be considered "unduly lenient".
The entertainer's age was one of the factors that influenced his sentence of five years and nine months for 12 counts of indecent assault.
A spokeswoman said the judge in the case also had to sentence Harris based on the maximum punishment available at the time of the offences.
It was also not possible to "simply add up sentences on individual counts" to reach a longer sentence, she explained.
"The overall sentence had to be just and proportionate to the overall offending," the spokeswoman added.
More top news
Andy Burnham warns far-left supporters of fellow Labour leadership candidate Jeremy Corbyn are putting party at risk of a 1980s-style split.
Ultimo underwear founder Michelle Mone is reportedly to be made a Conservative peer.
Charities could face criminal sanctions for bullying the public into giving money, their regulator has warned.