His remarks come days after his father, Emperor Akihito, was released from hospital after treatment for pneumonia.
He made the comments at a news conference to mark his 46th birthday.
“When you pass a certain age, it gradually becomes difficult for people to do various things,” Prince Akishino said.
He called for “more discussion” on establishing a retirement age for the emperor.
Emperor Akihito plays a largely ceremonial role but is respected deeply by many Japanese.
He spent almost three weeks in hospital earlier this month. He also had surgery for prostate cancer in 2003 and suffered stress-related health issues in late 2008.
Emperor Akihito has suffered from poor health in the past and has had a busy year in quake-hit Japan
. Under Japan’s 1947 Imperial House Law, the emperor is succeeded on his death by a male relative.
Crown Prince Naruhito is first in line to the throne, followed by his younger brother Prince Akishino.