FTO affects changes in BMI during both childhood and adulthood. However, its effect on onset age of overweight in adulthood is not known. To address this question, we conducted a study to examine effects of FTO tag SNPs on censored age of overweight in the longitudinal Bogalusa Heart Study (BHS) cohort, which began in 1973-1974. Of participating subjects, 658 whites (308 males and 350 females) with genotype data were selected for the study. The FTO gene was examined by a survival analysis of 30 tag SNPs regarding their association with left, interval and right-censored adult overweight. After adjustment for birth weight and sex, SNP rs9939609 has a small nominal p value of 0.004 for the association with onset age, which has an expected proportion of false positives of 9.6 % after adjusting for multiple tests. It was estimated that genotypes AA, AT and TT have onset age (standard error) of 22.82 (1.07), 28.96 (1.04) and 27.76 (1.04) years, respectively, for a 50 % cumulative proportion of overweight in the population. Genotypes AA, AT and TT, respectively, have estimated survival probability of 65.8, 78.7 and 76.8 % at the age of 18; and survival probability of 6.5, 11.8 and 10.7 % at the age of 60. The odds ratios of survival beyond age ≥18 years are 0.52 for AA versus AT and 0.58 for AA versus TT. We thus concluded that risk genetic variants at FTO gene can accelerate the onset age and influence the survival odds of overweight in younger adults.