According to the definition of max-width in the CSS 2.1 spec, “the effect of 'min-width' and 'max-width' on tables, inline tables, table cells, table columns, and column groups is undefined.” So you cannot directly set max-width on a td element.
If you just want the second column to take up at most 67%, then you can set the width (which is in effect minimum width, for table cells) to 33%, e.g. in the example case
td:first-child { width: 33% ;}
Setting that for both columns won’t work that well, since it tends to make browsers give the columns equal width.