More than a third of young people have debts of almost £3,000 and experience significant concerns about money.
A survey of 2,042 people aged 18 to 24 conducted for the Money Advice Trust by YouGov found that they borrowed using credit cards, overdrafts and loans from family and friends.
Just over half said they regularly worried about money, with 32% feeling their debts were a "heavy burden".
Women were much more likely to worry about money than men, the survey found.
The average debt of £2,989 excludes student loans and mortgages. The average student loan balance is £25,505.
National Debtline, run by the trust, says that too few young people are seeking free advice from debt charities when they fall into financial difficulty.
It has published a new report called Borrowed Years, which outlines measures that could help under-25s to better manage their money and avoid financial problems. They include:
- earlier and more co-ordinated financial education
- timely support for first-time borrowers or credit card holders
- a wider role for employers to support money management for young workers
- practical reforms to student finance payments
Joanna Elson, the trust's chief executive, said: "With many young people beginning to build up debts soon after they turn 18, we have a real battle on our hands as a society to make sure they receive the support they need.
"Worryingly, far too few under-25s are seeking advice when they fall into difficulty. If we let this situation continue, there is a real risk that young debts will become old debts, with the financial prospects and life chances of young adults being negatively affected as a result."
The research found that most young people try to manage their personal finances effectively.
More than two thirds (69%) of 18 to 24-year-olds have set a budget that they try to stick to and 71% check their account balance online at least once a week.
However, 37% of those in debt say they do not have a plan to repay what they owe, and 42% said they have found managing their money more difficult than expected.
Emma (not her real name), got a credit card after turning 18 and initially was able to make repayments, which led her provider to raise the credit limit.
But Emma became more reliant on her credit card and she began to spend more than she could afford. After losing her job at the age of 20, she could not afford the repayments and took out a loan in a bid to clear the £3,000 balance on her card.
After contacting National Debtline, its advisers explained the options open to Emma, which helped her get a better deal with her creditors and be "more sensible" with her money.
Ten top money tips for under-25s
1. Draw up a budget
2. Get more money in
3. Spend less where you can
4. Take care with contracts
5. Choose your bank wisely
6. Save if you can
7. Plan! Plan! Plan!
8. If you borrow, borrow safely
9. Look after your student finances
10. Get free debt advice if you need it from National Debtline or 0808 808 4000.
The Money Advice Trust was founded in 1991 as an independent charity with the support of the government, creditors and the advice sector.