Here is a link to IRS site that explains this. It specifically notes the case of a July 1st birthday.
https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-topics-required-minimum-di...
Your RMD year is 2019. You get a small extra time period for the first RMD, so you will need to take your first RMD by April 1, 2020. However, it is usually NOT recommended to wait beyond 2019 for your first RMD because you will have your second RMD, for Tax Year 2020, that will be due by December 31,2020. Taking 2 RMDs in the same tax year often bumps you into a higher tax bracket. So the normal recommendation is to take your first RMD in 2019 and your 2nd RMD in 2020.
