Final answer:
Babies who are slow to gain weight in the early months can potentially catch up by age 13, but this is not a scientifically proven fact and should be viewed as an assumption.
Step-by-step explanation:
The statement that 'No one has ever proven that babies who are slow to gain weight in the first few months of their lives generally don't catch up to their peers by age 13' leads to the conclusion that 'Babies who are slow to gain weight usually catch up with their 13-year-old peers.' The word 'usually' indicates that this is a general observation rather than a scientifically proven fact. Given the variability in growth patterns among children, particularly how growth can occur in spurts and is influenced by a range of factors including nutrition, genetic potential, and health conditions, it is possible for some children who are slow to gain weight in infancy to catch up by age 13. However, without specific data or studies to support this, the conclusion would be more accurately characterized as an assumption rather than a definitive outcome supported by evidence.