Wrong, Islam is the oldest religiopn in the world. Islam started with Adam, with the creation of man all prophets submitted to the will of God and taught their followers the same principles. Adam was the first prophet.
About hinduism being the oldest religion, you might want to read the history of hindustan written by persian/arab historians in the middles ages (500-1500 AD) none of these historians mention anything about hinduism or santana dharma.
Hinduism is a british invention created in 19th century, it was made a world religion in 19th century. at the time of the Arabs/Turks/Persians several distinct religions existed. I respect all religions but let let the truth be told,
Al Idrisi's description of Indian religions given above presents a clear description of the many different faiths practiced in India. He has accurately described the existence of Sun-worshippers (Rajput Sauras) and Atheists (Carvakas) as separate religions. None of the Arab travellers was aware of there being only one religion in India. This proves that `Sanatana Dharma' did not exist at that time.
Some of the Arab travellers even increased the number of Indian religions to 48:
" The Jamiu-l Hikayat increases the number of religions in India to 48 "
-- [ Arab.57.n1 ]
" Ibn Khurdaba has described that in India there are 42 religions
The Arabs adopted the Old Persian `Hindwa' as `Hind' (India) and `Hindwi' (Indian). Neither of these words were used as applying to any religion; they were purely geographical and national terms
Know the truth
The English Invention of Hinduism | truthofhinduism.com