Ok a few things to look at which may answer a few of the quibbles you are having.
1 its actually a size 6 blade with a short handle to make it size 5 length, so could the lad be built for a heavier bat but isn't very tall as in an adult wanting a heavier bat but is only 5'5'' that's one question to think about in an order which is why I talk at length with our customers about it.
2 these are made bespoke to customers requests and with some input from myself
3 its not just about weight its about feel. I make a lot of jnr bats for ex playing colleague's lads and lasses and have never had one say its heavy in whatever size weight range they have had as they know its down to pick up and feel. they know this from their own experience but we all know that the limits are less with jnr players due to strength.
4 you can go and buy any piece of old floor board out of a shop with a handle in it and the poor kid will be flogging his guts out trying to hit the thing off the square losing shape in all his shots. the skill in making these bats as perfect miniatures is to leave enough willow in them at the appropriate weight and feel that allows them to get full value in their shots whilst being able to hold shape throughout the stroke.
5 if after the young player has had a couple of hits and it does feel a touch heavy for him then we have the option of sending it in to remove a couple of ounces at just the cost of postage. we can always remove weight
6 I cant stick willow back on it to add the weight back
7 our success rate at making these bats for top young cricketers is easily 95% and the rest have all just been modified to suit and everyone is happy