Middle age begins at 35 and ends at 58. Middle age begins in your mid-30s and ends in your late 50s, a new survey finds. According to a study, the average Briton believes that youth ends at 35 and old age begins at 58. In between - all 23 years - is your middle age. The news that 58 is over the hill may come as a surprise to anyone who has passed the milestone and feels they are not yet in the twilight of their lives.