70, a study has found

When questioned by researchers, the post-war generation said on average they felt 'old' only after entering their eighth decade.
The findings suggest that in advanced years baby boomers retain（保持） their determination to cling to their youth. After drawing their pensions they are refusing to quietly see out their days as generations before them have.
Baby boomers, or those born between 1945 and 1963, have been called the luckiest generation ever after they enjoyed soaring house values, guaranteed pensions and lives of prosperity.
Their 'me generation' values spearheaded（带头，做先锋） the social changes of the Sixties and Seventies that left Britain changed for ever. More recently however they have also been blamed for a self-indulgence that has left the country financially, socially and even morally crippled.
The U.S. study found three quarters of all baby boomers considered themselves to be middle-aged or younger, even if they were in their 60s. The average age at which they said they were old was 70.
In general, baby boomers found once they reached their sixties it was nowhere near as bad as they thought. With improvements in healthcare they are able to spend more time with their grandchildren, travel and do the things they have been putting off for years because of work commitments.
The attitude of Marcelle D'Argy Smith, a baby boomer at 64, echoed the findings. She said: 'I wouldn't describe myself as old, I know I'm older and obviously not young.' The former editor of Cosmopolitan added: 'When you hit your 50s a new sense of freedom starts to creep（爬行，蔓延） in.'