Complex sentence: This is particularly untrue regarding alcohol dementia, the onset of which can occur as early as age thirty, although it is far more common that the dementia will reveal itself anywhere from age fifty to age seventy.
Split into simpler sentences: This is particularly untrue regarding alcohol dementia, the onset of which can be as early as age thirty. Although it is possible to acquire alcohol-related dementia early in life it is far more common that the dementia will reveal itself anywhere from age fifty to age seventy.