Simon Cowell started drinking and smoking aged eight.
The X Factor creator, 62, has also admitted he was a "nightmare" as a child and told how he once got arrested aged 12 for pointing a pea-shooting gun at a terrified bus driver in an attempt to hijack the vehicle.
He told The Sun newspaper on Sunday (30.10.22) about how he was a terror when he was his eight-year-old son Eric's age: "I was so bad when I was Eric's age. I was a nightmare.'
"I was drinking and smoking at eight, and I once nearly burned the house down.
"I was trying to prove to my brother that Father Christmas wasn't real, so I found the costume and set fire to the beard.
"I dropped it on the sofa and the sofa caught fire. The whole room went up.
"Luckily, my older brother smelled the smoke and found us. Then the fire brigade came."
Talking about his arrest, Simon, who shares Eric with fiancée Lauren Silverman, 45, added: "I stole my dad's car at ten and crashed it. Then when I was 12, I hijacked a bus with a pea gun.
"I thought it wouldn't be taken seriously, but the driver called the police and I was arrested. I remember going back home and my mum being furious.
"She was the disciplinarian, my dad was always the softer one.
"He said so many things that stuck with me, but I can't remember him ever raising his voice to me.
"But I was so bad, slightly living on the edge. I was smart, but I wasn't academic at all. I could have never been a doctor and I had a very low boredom threshold.
"So it was school after school, and then I was out at 16."
Despite his antics, Simon also said he was "unbelievably shy" as a youngster.