From the date of this answer (9/23/2018)... 1 year, 5 months, and 23 days. An exhibition game was played between the Atlanta Braves vs New York Yankees on 3/31/2017. But literally the park was completed with everything on 3/8/2017, which would give the park's age of completion to now as 1 year, 6 months, & 15 days.
2018 is the second year that the park has been opened. The Braves played their final game at Turner Field in 2016. They played their first game at Suntrust Park in 2017.
Thanks! Your answer is awaiting moderation.