When Plotted on an H-R Diagram, the More Massive Stars

When plotted on an H-R diagram, the more massive stars of a particular star cluster are on the main sequence and the less massive stars are above the main sequence. Can the age of this cluster be determined? (In other words, how long is it since these stars condensed from the interstellar medium?)

A) Yes, by finding the most massive star that is on the main sequence. The age of the cluster equals the time this star spent as a protostar.
B) No.
C) Yes, by finding the least massive protostar. The age of the cluster equals the time this star took to reach the main sequence.
D) Yes, by finding the least massive star on the main sequence. The age of the cluster equals the time this star spent as a protostar.