Voice onset time (VOT) is a temporal acoustic parameter that reflects motor speech coordination skills. This study investigated the patterns of age and sex differences across development of voice onset time in a group of 70 English-speaking children, ranging in age from 4.1 to 18.4 years, and 12 young adults. The effect of the number of syllables on VOT patterns was also examined. Speech samples were elicited by producing syllables /pa/ and /pataka/. Results supported previous findings showing that younger children produce longer VOT values with higher levels of variability. Markedly higher VOT values and increased variability were found for boys at ages between 8 and 11 years, confirming sex differences in VOT patterns and patterns of variability. In addition, all participants consistently produced shorter VOT with higher variability for multisyllables than monosyllables, indicating an effect of syllable number. Possible explanations for these findings and clinical implications are discussed.