Characters
I think adults are just children who owe money.
— Andrew · Peter's Friends
Behind the line May contain spoilers.
Our reading
An editorial interpretation.
Adulthood is reduced to a financial obligation rather than a transformation in character. The suggestion is that the child remains, with debt added on top. Its humour comes from deflating the dignity of being grown up, replacing assumed maturity with the less flattering fact of owing someone money.
Context reviewed