My DS was 12 months when he point blank refused to let us feed him anymore - he is now 20 months and quite accomplished with a spoon and fork (not let him near a knife just yet ).
However, I was recently talking to am acquaintance who has a DS a month older than my DS (so 21 months now) and she doesn't let him feed himself as it (a) takes too long and (b) makes a mess so she still spoon feeds him - surely a 21 month old should be feeding himself?