Well, if a 20+ 200 meter runner is training at a 28 pace, then he is training at 60% of his maximum. A less qulified runner, say a 23+, would therefore train at 32 seconds, which is 60% of 23.
Of course, as Charlie has pointed out, a person’s maximum fluctuates dependent upon dozens of variables, so that always must be kept in mind. A set of 28 200 meters may be hard for a 20 athlete at certain points of the season.