What age do toddler dress and undress themselves?

my toddler is the same age. he can pull down his pants on his own but needs help with taking off tops (just the arms part then he will take off himself). me and hubby practice letting him be independent as we feel that it's the right age. even if we help him with something, we will show him how it's done step by step & let him continue finishing it. but , as other mentioned , each kid has different milestones so don't worry too much about it!