You cannot determine the age of a "texture". There are numerous methods for dating the age of rocks. Go to Geology.com and search for rock dating methods.
Porphyritic textures are formed when magma begins to cool while it is still underground. Minerals that crystallize at higher temps will start to separate out and form crystals. As the magma cools,...
There have only been estimates on the ages of celestial objects, but some things need a certain amount of time to form, opening doors for educated guesses.