A limitation of the morningness–eveningness literature is the assumption that morningness is a ‘fixed’ construct. Morningness–eveningness scales are often developed on young adult samples, yet studies report that eveningness peaks in young adults with a shift to morningness from the age of 25 to 35 years of age. This age related change in morningness–eveningness may explain why these scales have limited success when applied in older samples. We tested this argument by developing a measurement model based on the Composite Scale of Morningness using a sample aged <30 years of age. Tucker’s congruence coefficient and confirmatory factor analysis indicated this solution was not a good fit in three older age groups. In contrast, we repeated this assessment using the ‘morning affect’ scale. This scale comprises items that measure morningness preference only. Model fit indicators suggested the ‘morning affect’ scale was a good fit across four age groups and gender.