Larry's head is full of gas and there is no brain in there (since he's a basketball) and keeps popping his head somehow so he usually carries around bandages.

He really loves energy drinks and will drink it regularly like it's water and he's been doing this for years until when he got to fosters he was forced to stop

As soon as Wilt lost his arm and eye after the game Larry kind of got abandoned by his creator since he had no purpose anymore and Larry would usually chill or stay at the top of abandoned buildings and he would use arrogance, reckless behavior, and bullying to cope with loneliness and he'd push others away

He likes chicken grilled sandwiches

I know imaginary friends can't age physically but when they are like say in a relationship and married, because in my headcanon they can get married, they can choose to die along with their soulmate. Or when their adopter is ill and dying they can choose to pass on with them. Their bodies won't disappear either so they can either be cremated or baried along with their loved one.

The imaginary don't disappear when their creator passes on, but they can choose to do so. So they are technically immortal.