Joel Maunder, 18, was more than twice the legal limit when he was stopped driving his parents' 15mph mower on his way to meet friends.
He had already driven the 125bhp £1,700 ride-on machine nearly a mile from his home before he was caught.
Richie Paul for the prosecution told Barry magistrates court: "He was slowly travelling down a road when he was spotted on the Lawnflite vehicle by police. He was breathalysed and found to have 83 micrograms of alcohol in 100 millilitres of breath, the limit is 35."
Joel admitted the charge of drink-driving in his home village of Dinas Powys, near Cardiff.
His mum Esther, 42, said the case had all been "very embarrassing for us."
Do you think a 17-month driving ban is appropriate for this crime?