Your first required minimum distribution must be taken by April 1 of the year following the calendar year in which you reach age 70½. Since you reached age 70 1/2 in 2017, you have until April 1, 2018 to take the first distribution.
Keep in mind that if you wait until 2018 to take the first distribution, you'll be required to take a second RMD for 2018, so it may be preferable to take the first RMD in 2017. The IRS explains:
The first year following the year you reach age 70½ you will generally have two required distribution dates: an April 1 withdrawal (for the year you turn 70½), and an additional withdrawal by December 31 (for the year following the year you turn 70½). To avoid having both of these amounts included in your income for the same year, you can make your first withdrawal by December 31 of the year you turn 70½ instead of waiting until April 1 of the following year.
Example: John reached age 70½ on August 20, 2013. He must receive his 2013 required minimum distribution by April 1, 2014, based on his 2012 year-end balance. John must receive his 2014 required minimum distribution by December 31, 2014, based on his 2013 year-end balance.
