I said he's healthy...
2 scenarios where he’s always been healthy -
1. The other siblings simply had a bris first. The minhag is to do the oldest first, but I didn’t see a Halacha against it. But the better answer is -
2. The oldest son was born Ben hashmashot Friday night, with a delayed bris until Sunday, while the others were born on Shabbos. Hence the other siblings had an earlier bris.