Is there any non-Tamilian who believe that the Tamil language is older than Sanskrit?

Vedic Sanskrit is believed to have existed before 600BC, whereas Tamil has earliest written history in 500BC though origin of these languages are unknown given both the languages are termed as pre-historic languages.

However, there is little clarity on which REGION that SANSKRIT originated, thrived and travelled. Either Sanskrit or its photo/earlier version might have originated in Caucasian region that gave way to many Indo-European languages and it might have evolved into more matured form ie., vedic Sanskrit with Devanagari in present day Afghanistan/Iran before moving into India, Nepal and east Asian countries. Many terminologies (eg. soma - a type of intoxicating drink) used in Sanskrit are still in use among tribes living in Afghanistan and Iran. Also, much of the products in Sanskrit passed on from one generation to another orally or through vedi education.

Whereas, Tamil originated and evolved within Indian regions. There is no definite timeline indicated its origin, but earliest inscriptions date back to 500BC. The common reference to pre-historic form of Tamil is Proto-Dravidian however given its pre-historic nature, we cannot conclude it was a different form of language or definite existence of Tamil itself before the available evidences.

Interestingly, the study on gene patterns among various Indian races, the earliest pattern has been recorded among tribes living in present day Kerala's Agasthiyakoodam hills. (note, Kerala was an integral part of Tamil linguistic region until 13–15th centuries). Coincidentally, much of early Tamil literatures point to the very same region - Podhigai hills - as the place where Tamil originated, with stories like Sage Agasthiya gave birth to written form of Tamil. Tamil is the least adultered Dravidian language while other Dravidian languages have undergone varying level of Sanskrit influence that led to the evolution of those languages, or even formation of new languages eg., Malayalam - a language that was a dialect of Tamil evolved into a new distinct language in 13–15th centuries due to influx of brahmins from Northern India (or, may be exodus due to Muslim rule in the north)

In a nutshell, Sanskrit may or may not predate Tamil, but Tamil definitely predates Sanskrit within Indian region. Also, antiquity of Sanskrit is perceived/understood through vedic scriptures and epics that were passed on from one generation to another orally or through vedic education system. While, Tamil's origin is explored through inscriptions on rocks, palm leave manuscripts and the remnants of ancient kingdoms like Early Pandyan Empire.