5 month old still using ss teat size

Hi mummies, my lo is reaching 5 months old and is still using pigeon ss teat size. Tried changing the teat size to s size previously when she reached 3 months plus but baby was crying and choking. She usually take 15 to 20mins to finish her milk. Recently my mil mentioned to change her teat size since she is going 5 months and should be using m size teat instead. Tried changing her teat size but she was crying real badly and refusing to drink the next day. Just to check, is it normal for 5 month old to still use ss teat? #advicepls #1stimemom #firstbaby #JustMoms