Mikayla from Secret Lives of Mormon Wives has discussed that she became pregnant as a teenager, and online reports and forum discussions consistently say she was around 16 years old when she got pregnant.

A widely shared Reddit thread about the show states that she “became pregnant at 15 and gave birth at 16,” and other viewers describe her as being pregnant at 16 (possibly giving birth at 16 or 17, depending on the exact timeline). An article breaking down her relationship with Jace notes that they met when she was 15 and he was 20, and that she became pregnant within about a month of dating, when she was 16 and he was 21.

So, based on publicly available reporting and fan discussions, the best- supported answer is that Mikayla was about 16 years old when she got pregnant.

Information gathered from public forums or data available on the internet and portrayed here.