17 and 8 months. This has been a constant source of heated discussion in our family. We are probably one of the few parents who put our son a year up in school. We homeschooled him until 2nd grade, and instead of putting him in 2nd grade in school, we put him 1 grade up to 3rd grade bec his can handle it academically and socially. He had no issues in school and has a great group of friends (some who are 2 years older than him). However, he's always been on the smaller side (size wise). And when he sees his metrics compared to his class (2023) vs. his age group (2024) or even 2025 (if he gets held back a year), he gets so frustrated with us as he feels like he would have been highly ranked in the state as a 2024 or 2025.
My wife and I never regretted the decision. We tell him that he gets a 1 or 2 year head start in life (and earnings), he has 1 or 2 more years to enjoy adulthood and his family later on, he has an amazing group of friends that he would not have been with, and he probably would not have met his current GF (that last reason is the one that works the best with him...). Baseball wise, I tell him that he probably would not have gotten to where he is right now (skill wise) if he has not been forced to work harder to keep up with kids bigger than him. I tell him that he will find the right college for him, and at some point in the near future, everyone will reach their maximum growth and the playing field will become even. He would have an advantage then as he's always had to work harder growing up. He may not have gotten the attention or accolades when he was 12 to 16 years old, but that's not what's important.