This may be due to Peyronie's disease, With age there is a decrease in the elasticity of collagen fibers which can also lead to scar tissue.
Weak and poor development of the corpora cavernosa (Spongy tissue) is another cause of penis curvature. The penis consists of spongy tissue called the corpora cavernosa. If the little openings in the spongy tissue on one side of the penis develop to a lesser degree than that on the other side then the lesser-developed side will have stronger blood circulation. This increased blood flow would force the penis head over the furthest point of leverage, causing a curved or banana shaped penis
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I would however suggest seeing a urologist to confirm.
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