depends on what the clothing is. Socks are fair game from about 6mths, as are nappies sometimes (oh boy they can be messy, babies lol).
pull-up trousers from about a year/ year and a half, t-shirts too.
Althought they expect your child to be doing certain things by a certain age children will only go at their pace and do things when they are ready. Go with the flow and if you are concerned that maybe a child is a little slower than you would expect then try to turn the dressing and undressing into a game - I found getting dressed or undressed with my children a big help in encouraging them cos it would be a race, with a treat at the end of rthe "winner" (always the child lol).
hope this help, hugs to you. xxx