Gday Evosy

It is quite difficult to tell you that your current condition is from childhood, genetics, a combination of both etc. and to be honest I am not sure the origin is the MOST important thing currently. People with sway backs can have unusually high stresses on their spine, especially their lumbar spine, due to the poor positioning of the vertebrae. Seeing as you are a plasterer, your job involves a lot of postural tolerance positions, i.e. leaning forward repetitively, overhead work etc. again putting a lot of force through the spine.

Do you currently have any back pain? Or issues which might require our attention? Or are you mainly after a solution to "correct" your sway back? It is quite difficult to alter the shape of your spine, and almost impossible to do it in any "short" term, unless the cause is severe muscle imbalance (i.e. extremely tight hip flexors / tight QL + weak hamstrings etc.) However, you can train some of your muscle systems to better support your back, and their are a lot of good postural exercises around.

Let me know exactly what solution you are after from this post, and I will reply more specific to your requests, rather than talking about genetic predisposition to postual toleraces and low back pain etc. which will take this thread in a completely different place. Thanks!