Behavioural studies of children with specific language impairment (SLI) have reported long-term growth outcomes across different dimensions of language. Genetic studies of children with SLI have identified candidate genes and putative associations of gene variants with SLI. The aims of this review are to summarize these two lines of investigation and to highlight the possible role of underlying growth timing mechanisms that influence the trajectory of language outcomes throughout childhood and into adolescence. Behavioural growth trajectories demonstrate that children with SLI have notable strengths in language acquisition, as well as limitations, across different dimensions of language. Language onset appears delayed, although the rate and pattern of change over time is similar to unaffected children. Growth rate decelerates early in adolescence for some dimensions of language. Genetic investigations reveal candidate genes that are known to influence neuronal development, and reveal possible gene interactions along a causal pathway. Epigenetic studies reveal other genetic influences implicated in the cognitive decline associated with ageing. This review highlights possible parallels between underlying genetic mechanisms and characteristics of linguistic growth trajectories. The conclusion is that new developmental perspectives are needed to inform language intervention in ways that align nurture with nature.