G.T.
After 5 1/2 months do you really have to be that specific? How about when someone asks how old he is just telling them he is about 5 1/2 months old.
My kids are all grown and when a new mom asks when they did certain things I usually say something like, they walked when they were about 10 months old, or they potty trained at about 2 1/2 years old, or they went to school at around 5 years old, etc. I knew a woman once that drove people nuts with stats about her kid. She could tell you the age her son did something down to the day (ie: He took his first step at 11 months, 2weeks and 3 days). It got to the point no one wanted to ask how old her kid was or when he did certain things.