There is growing evidence that the prenatal environment has long-term effects on adult grip strength, but little is known about the effects of the postnatal environment. We tested whether prepubertal growth, pubertal growth, or the development of motor and cognitive capabilities was associated with midlife muscle strength independently of other determinants of grip strength. Handgrip strength and body size were measured in a representative British sample of 1406 men and 1444 women 53 years old with prospective childhood data. Normal regression models were used to examine the effects of birth weight, postnatal height and weight gain before 7 years and between 7 and 15 years, motor milestones and cognitive ability on grip strength at age 53, taking account of lifetime social class, current physical activity, and health status. Birth weight and prepubertal height gain were associated with midlife grip strength, independently of later weight and height gain and other determinants. Pubertal growth was also independently associated with midlife grip strength; for men weight gain during puberty was beneficial, whereas for women it was height gain. Those participants with earlier infant motor development had better midlife grip strength, which was partly confounded by the growth trajectory. This study showed that components of prenatal, prepubertal, and pubertal growth have long-term effects on midlife grip strength. To the extent that these associations are modifiable, interventions in childhood that help to build muscle mass and strength, such as increased physical exercise, may have long-term beneficial effects on adult muscle strength and may help to prevent sarcopenia, disability, and frailty in later life.