Do you know how to tell a difference between 3.5 and 4.5 yo? Ask a kid to catch a ball. The eye-hand coordination is much better in 4 yo.
When my daughter was learning to catch a ball, we did not use a ball, we used a ... balloon! Yes, that's right, regular air filled ballon.
A ballon falls slower, giving a toddler a change to track it with his eyes and get his hands ready for catching. It also it lightweight and easy to hold. And it's won't break the chandelier should it be thrown too high.