The number-one songs on the Hot 100 in 1969 were by, respectively, Marvin Gaye, Tommy James & The Shondells, Sly & The Family Stone, Tommy Roe, 5th Dimension, Beatles, Henry Mancini, Zager & Evans, Rolling Stones, Archies, Temptations, Elvis Presley, 5th Dimension (again), Beatles (again), Steam, Peter Paul & Mary and Diana Ross/Johnny Bristol (although the label credited Diana Ross & The Supremes).
I'm pretty sure I know the answer now. The lead singer of one of those groups was 33 when they first charted. I'm also pretty sure somebody here will figure out the answer and post it before I do. If that happens, I won't be angry. I won't consider that person to be an arch-villain.