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The subject of intentional breeding or meat rabbits is prohibited. The answers provided on this board are for general guideline purposes only. The information is not intended to diagnose or treat your pet. It is your responsibility to assess the information being given and seek professional advice/second opinion from your veterinarian and/or qualified behaviorist.
I fixed your posts for you. There are issues with uploading pics from mobiles, sometimes they don’t show so all you need to do once you have posted is click on “edit” on your post and then re-submit the post. I removed the pics from your other post because they were the same as the ones you already posted 
Unless rabbits are quite overweight, it can be difficult to visually see whether they are a correct weight, especially when they may be a little underweight the fluff tends to hide that. You need to assess his weight by feel. Pet along his back, you should be able to feel the spine and hips without applying much pressure, but they shouldn’t feel sharp. They should feel cushioned by a thin layer.
Here are a couple of guides:
http://charlotte-harris.net/wp-content/uploads/2013/12/Body-Condition-Score-Rabbit.jpg
http://www.therabbithouse.com/diet/images/rabbitweightbodyscore.png
If you suspect he is thin, are you also feeding him pellets? Pellets are the best thing for keeping/putting weight on a rabbit. I know some people don’t feed pellets and simply feed hay and a wide variety of leafy greens, but I think for growing rabbits pellets should be added just to ensure they get all the nutrients they need. Some adult rabbits (like my Luna) don’t maintain weight well without pellets even when getting a large variety of greens every day.
Australian mini lops are different to those overseas. Our mini lops are similar to the USA Dwarf Lop although , and our Dwarf lop is like the USA Holland Lop. (At least I think that’s the way it is, I get confused and never remember it properly). From what I’m reading though, Aussie mini lops are around 1.5kg adult weight, so I feel like your boy should weigh more by now. When my previous rabbit was about 4 months, he weighed about half of his final adult weight.