Complex sentence: In the United States, 20% of the population will be older than 65 years of age by the year 2030, with those 85 years and older being the most rapidly growing group The Oldest Old.
Split into simpler sentences: In the United States, 20% of the population will be older than 65 years of age by the year 2030. Those 85 years and older will be the most rapidly growing group The Oldest Old.