Lot of old timers had good/great performances past 40. Robinson, Moore, Walcott to name a few. For more recent times there is Holmes-Mercer.
Carlos Palomino got his first 1st round KO as a 48-year old against former WBC 140-lb champ Rene Arredondo
From This List, BHop Over Tarver... Tarver was a More DANGEOROUS Opponent than Any of the Others Listed... REED