Ultimately it is up to him. I say buy a package of the #2 nipples and try it. You'll know right away if he can handle it. That's what we did and we found that it took our guy quite a bit longer than I thought it would for him to go up to a medium flow nipple. I just kept trying. Have you ever noticed that he sucked so hard that it flattened out the #1 nipple? If so he may be ready to go to the #2 size.
I know that for my daughter, I think I switched her to #2 nipple around 4 months. But then she satyed on them until she was 11 months. I tried to switch her to #3 several times but she was also choking and it was coming out too fast for her. It will definitely take your little guy a few days or so to get used to the new nipple, just be patient. Good luck
Hi. Generally, #2 nipples are for 3 to 6 months, and #3 nipples for kids older than 6 months. I started using the #2 nipple at closer to 4.5 months just because I was afraid the baby would choke if I switched too soon. Since your baby is 5 months now, you can try switching to #2 and see how he reacts. If can't keep up or starts the milk, you'll know it right the way. Otherwise, if he takes it down no problem, that'll be your answer. Also, I just switched to the #3 nipple and my girl will be 8 months tomorrow. The milk flows fast but she is handling it great and it cuts down the feeding time in half, literally.
These nipples can be pulled out—though not as easily—through the same manipulation method as Grade 1 nipples. However, Grade 2 nipples retract back into the areola after finger pressure is released. Breastfeeding is possible with Grade 2 nipples, but will present problems.