Twitter’s US user base shows signs of maturing in its demographic composition, spreading the user population more evenly across age groups, while Instagram is still largely limited to a pool of millennial and Gen X users. Last year, 69.0% of Instagram’s users were ages 18 to 44. This year, that figure will drop, but only to 67.5%, and over time, Instagram’s user base in these age groups will approach, but not surpass, Twitter’s. eMarketer does not expect significant shifts in usage by age for either site within our forecast period, and Instagram’s user count among 18- to 44-year-olds will remain about 1 million fewer than Twitter’s in each year throughout our forecast. Read the rest at eMarketer.