There have been many brother acts in the illustrious history of rock & roll, in large part, I suspect, because someone's mother made them drag their little brother along just so she could get some peace in the house. The upshot is that many bands of brothers end up making their first record when the youngest isn't even out of his teens. Thus,
The Everly Brothers had their first Top 40 hit ("Bye Bye Love") when Phil was just 18.
The Isley Brothers wrote and recorded the iconic "Shout" (which didn't make the Top 40) when Ronald was just 18. Marvin Isley joined the group in time to perform on the Top 40 hit "That Lady (Part 1)" when he was just 19.
The Beach Boys had their first Top 40 hit ("Surfin' Safari") when Carl Wilson was just 15.
The Ronettes recorded their first Top 40 hit ("Be My Baby") when Ronnie Spector was just 19.
The Shangri-Las had their first Top 40 hit ("Remember [Walkin' in the Sand]") when Mary Weiss was just 15.
The Kinks had their first Top 40 hit ("You Really Got Me") when Dave Davies was just 17. Ray and Dave, by the way, had six sisters but no other brothers.
The Bee Gees had their first Top 40 hit ("New York Mining Disaster 1941") when Robin Gibb and Maurice Gibb were both 17.
The Cowsills had their first Top 40 hit ("The Rain, the Park and Other Things") when drummer John Cowsill was 11. He was also in Tommy Tutone.
The Jackson 5 had their first Top 40 hit ("I Want You Back") when Michael was 11.
Wilson Phillips had their first Top 40 hit ("Hold On") when Wendy Wilson was 20.