Listeners are able to rate a speaker's age with reasonable accuracy. Although several speech features are known to be characteristic for specific age groups, there is less knowledge about the perceptual relevance of that parameters. This paper describes the results of a perception study, where single word stimuli were synthesized and rated regarding the perceived age by 20 listeners. All combinations of pitch and speech rate were synthesized with male and female voices. Results show that speech rate had the largest impact on listeners' judgement. Although pitch variations alone did not show a large impact on listeners' judgements, significant differences between selected pitch levels at slow and fast speech exist. Our results contribute to the identification of the relevant features signaling a speaker's age. Results further support the assumption that a set of parameters almost always interact in signaling a speaker's age.