No idea how old.

[williamh]

This looks like the typical early 20th century export plate but older and of much better quality. Any help is appreciated.

[peterp]

The foot rim has grit and a shape that would fit into the late 18th century (Qianlong). Celadon based decorations like this, showing butterflies and other insects were common in the Jiaqing reign. We know that early in that reign they still did use some blanks fired during the Qianlong dynasty. That is why some early 19th century items have this type of base. Otherwise the foot rim should be straight up.