  We investigate techniques that can be used to determine ages of starburst
regions containing populations beyond their early nebular phase. In particular,
we study the strength of the CaII triplet (lambda 8498, 8542, 8662 Ang) and the
CO index (2.31-2.40 micron band) using synthetic models as the starburst
evolves. For an instantaneous burst of star formation both of these absorption
features remain strongest between 7-14 Myr corresponding to the red supergiant
population. The detailed evolutionary behavior of the starburst is strongly
metallicity dependent. Low metallicity starburst models successfully reproduce
the distribution of equivalent widths of CaII triplet with age in Large
Magellanic Cloud clusters. The clusters in the red supergiant phase strongly
favor the stellar evolutionary models incorporating mass-loss rates higher than
the standard values. We suggest usage of diagrams involving CaII triplet
equivalent width, CO index and nebular recombination lines to infer the history
as well as age of starburst regions.
