We first clarify the definition of sustainable employability, and then we study how the indicators of sustainable employability among older Finnish postal service employees have changed over time. Finally, we estimate the effect of age on these indicators in a two-year follow up. A questionnaire survey among the Finnish postal service employees was conducted in 2016, and a follow-up was conducted in 2018. We analyze data from 1262 subjects who replied to both the baseline and the follow-up surveys. Sustainable employability is defined as a multidimensional construct using nine indicators and covering three domains (health, well-being and employability) based on Fleuren and colleagues' model. Measurement time (repeated measure) is used as a within-subjects factor, and age is used as a between-subjects factor. The estimated marginal means of the indicators of sustainable employability at the baseline and the follow-up by age in years are calculated. No significant change is found in eight indicators (work ability, time and resources, recovery after work, job satisfaction, motivation, perceived employment, enough training on the job and relevance of work) of sustainable employability after the two-year follow-up. We find a statistically significant effect of time on self-rated health (F = 6.56, p = 0.011). Six out of nine indicators (self-rated health, work ability, time and resources, recovery after work, job satisfaction, and perceived employment) have a statistically significant effect of age between subjects. Partial Eta Squared  (ŋ²_p) shows a very small difference in the indicators of sustainable employability during the follow-up, indicating that the employability of the workers was sustained throughout. We used the Fleuren model as the basis for our definition of sustainable employability. Although they are based on single items, these indicators of sustainable employability remain stable after the two-year follow-up. Significant effects of age between subjects are found for six out of nine indicators. The results suggest that age may be an important determinant of sustainable employability.