Modern Russian is a little bit older than hundred years.
"Pre-reform" language was significantly different in script, vocabulary and grammar and wasn't older than hundred years itself. Before Napoleonic war 1812 nobility was speaking French, ruling family was German and serfs were speaking Polish, Belarusian, Ukrainian or one of the Turkic dialects.
The only slavic parts remaining in the modern Russian is Cyrillic script and words borrowed from Ukrainian.