Jack Garnett, of Kings Drive, Carnforth, appeared before Preston Crown Court where he entered a guilty plea to a charge of sexual activity with a girl under 16.
The offence happened on September 4 last year in Carnforth.
The youngster cannot be identified for legal reasons.
The case had suffered a delay due to the coronavirus pandemic affecting the courts.
Judge Robert Altham adjourned the case to November 9, when it is expected the 25-year-old defendant will be sentenced.