Little things such as finding a fuse box when the lights go out, meeting a bank manager for the first time and setting up direct debits to pay bills are also signs of finally growing up, it adds.
Up to then most young adults are probably living at home or university and not had to worry about the more mundane responsibilities in life.
But when they suddenly find themselves doing the weekly shop or cooking their own meals, they feel grown up, said the survey of 2,000 18-25 year-olds by online sale site Gumtree.
It is also the point at which they find life is more expensive.
This age group collectively spends £1 billion a year in simply trying to get that first full time job, from the amount spent on clothes and hair to look the part to travelling to get to interviews.
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More than one in four (27 per cent) have not applied for some jobs because of the travel expenses to the interview and 38 per cent have not gone for it because of what it would cost to commute if they got it.
Growing up also means the shock of finding out just how much it costs to move out of home and rent or buy a property, particularly in London, said the survey.
Hannah Wilson of Gumtree, said: “We know that making the fully-fledge transition into adulthood is expensive.
“Moving out and taking on a newfound sense of responsibility and the search for that first or ideal job can take its toll on young people both financially and emotionally.”
WHAT MAKES 18-25-YEAR-OLDS THINK THEY ARE A ‘PROPER ADULT’:
1. Setting up direct debits to pay bills (46 per cent)
2. Doing the weekly shop (42 per cent)
3. Owning a car (41 per cent)
4. Buying your own furniture (38 per cent)
5. Cooking a meal from scratch (29 per cent)
6. Meeting the bank manager (23 per cent)
7. Locating the fuse box (23 per cent)
8. Making pack lunches for work (21 per cent)
9. Getting your clothes dry cleaned (17 per cent)
10. Changing a lightbulb (16 per cent)