Unless you have one of the few rare CBB bosc monitors (been a few years since it has been done in this country) you have a wild caught animal, therefore you have no clue how old it really is. I used to be involved with the pet industry and rescueing selling reptiles, supplies etc many years ago. Its common place for a wholesaler to buy hundreds of bosc and nile monitors one year, then sell as many as possible (hatchling size, unknown age), then keep the rest until next year arely ever feeding them, and keeping the survivors cool to keep them from growing, why, simple to sell them as this years babies next year or all year long.
Next male bosc grow larger than females, the male can grow to sizes of 3ft or more from a 5 inch baby in one year (not the best husbandry by a stretch either), then into a 4ft plus monster by the second year, then a few can go beyond a few inches.
A long time ago I stopped seeking out WC monitors and reptiles to keep, its easier to keep CBB animals, cheaper in the long run and the selection avaiable are more expensive more fascinating species to pick from.
I guess best of all I have the satisfaction that I am not contributing to the WC reptile industry and those thousands which die in the first days to a year they are kept.