Sinckler is one of several players, such as Owen Farrell, Jamie George, Manu Tuilagi and Courtney Lawes, who have passed their 30th birthday.
Jack Willis, David Ribbans, Henry Arundell and Joe Marchant will play in France next year and may be ineligible.
"It has been mentioned - the 'last dance'. It makes everyone aware how special this is," said Sinckler.
"It will never happen again."