We oldest layer of the Vedas gives you 3,500 years at the utmost. But how many modern Hindus read the Vedas, or do Vedic sacrifices?
Well, it kinda depends what practices we are talking about.
Bhakti didn't even come about until the CE era.
The four aims of Hindu life? Originally, there were only 3 (moksha was added later).
Knowledge never exists in a vacuum. So, seriously, why do you want to know? Why does it matter? There are good academic reasons to query Hinduism's age. But most people aren't academics.