Sullivan grew up on screen instead of having a normal childhood. Outside of the nastiness of the industry and the pressures of fame, growing up on a tv set would have been fucking mind-numbingly boring. I did a local am-dram thing with a friend once, as she didn't want to go alone. I thought it might be fun. But fucking hell was it unbelievably boring. Reading through the same scenes over and over to memorise lines, practising without the script, working out the blocking, etc, and on tv, having to do the same scenes over and over even once they're prefect and doing everything out of sequence, so the story doesn't even make sense to you. The kid was only eight years old when he had to start doing that as a full time job, presumably on top of school work. It's a shit way to grow up, and it's not surprising that as soon as he hit adulthood he opted out completely.