No but baby beardies have been known to bite each other's tail off by accident in play
no...much much smaller
Reported size is up to 20 inches for an adult (including the tail)
it's not unhealthy if that's what you mean.
It means you should not be housing your bearded dragons in the same enclosure, and need to IMMEDIATELY separate them into their own enclosures. Also, the dragon with the missing tail should see a vet.
Take it for treatment to a qualified animal doctor (a vet).
A fully-grown Bearded Dragon CAN be as much as 14 inches nose-to-tail. It's rare for them to get to that size though - the 'norm' is around ten inches.
Most dragons had a tail, it is not exactly known if ALL dragons had a tail.
it depends on their body condition because they have fat pads in their tails, but usually males will have a wider base of the tail and females will be narrower
no it has an actual snake for a tail
The term juvenile, when refering to reptiles specifically the bearded dragon, is any stage in between when he is still a baby (Under six inches without tail) and when he is full grown, (aprox twenty inches without tail). so there is a fairly large size range for your beardie to be still considered a "Juvenile*
No. Bearded Dragons don't have the ability to regenerate and many adults have missing toes and tail tips from accidental nipping by their siblings when young. It takes time for Beardies to become accurate hunters and to be able to differentiate between moving food and that which is not food. If purchasing a Beardie, please find a good breeder who has raised their babies in optimum conditions and therefore made an effort to minimise injuries. If purchasing more than two babies to keep together, ensure they never become hungry! A BD with a full tummy is less likely to instinctively strike at moving objects on the off chance that it may be food.
It means that they are not getting enough calcium, uva light and uvb light. I recommend asking a reptile veterinarian. But it could also be a genetic deformity that is natural.