How old is Sanatan Dharma ?

Sanatan dharma is the first religion to be invented.it is also known as Hinduism.It is so old that it's founder's name or specific period is unknown.Still it would be millions of years old.Lord Krishna first taught it to Suryadev.Among its roots is the historical Vedic religion of Iron Age India, and as such Hinduism is often called the "oldest living religion or the "oldest living major religion".Vedas reveal this truth which are the sacred books of Hinduism