The performance of early-maturing breed sired suckler bulls finished at pasture, with or without concentrate supplementation, at 15 or 19 months of age was evaluated. In total, 60 Aberdeen Angus-sired bulls were assigned to a two (slaughter age (SA): 15 (S15) or 19 (S19) months)×two (finishing strategies (FS): grass only or grass+barley-based concentrate) factorial arrangement. There were no (P>0.05) SA×FS interactions. Increasing SA increased carcass weight (265 v. 355 kg), kill-out proportion (542 v. 561 g/kg), conformation (6.7 v. 8.3, 1 to 15) (P<0.001) and fat (5.8 v. 6.8) scores (P<0.01), and resulted in yellower subcutaneous fat (‘b’ value, 6.6 v. 8.3) and darker muscle (‘L’ value, 30.0 v. 28.3) (P<0.01). Supplementation reduced estimated herbage intake by 0.60 and 0.47 kg dry matter (DM)/kg DM of concentrates for S15 and S19, respectively. Supplementation increased carcass weight (+6.7%, P<0.001) and kill-out proportion (+1.8%, P=0.06) but had no effect on carcass fat and conformation scores or fat and muscle colour. In conclusion, carcasses were adequately finished, with or without concentrates for S19, but not for S15. Supplementation had no effect, and age had relatively minor effects, on fat and muscle colour.