Frank Sinatra and Elvis Presley didn't had childish voices. Their voices sounded like men. Their voices were not too high for a mature listener to listen to.
Yes, Elvis and Frank had teen girls back in the day but that was something different. It was something different and fresh. Frank Sinatra was the first teen idol. Frank Sinatra voice wasn't very high or didn't sound like a kid.
As for Elvis, Elvis sang and played Rock and Roll music. Rock and Roll was known as a bad influence back in the 50s. Many adults actually thought the genre would have a bad influence over the kids. Rock and Roll was louder than most of the mainstream genres at that time in the 50s.
Justin Bieber in the other hand is just another Pop singer. He didn't sang nothing new. I mean, Frank Sinatra didn't sang nothing new either but his voice is really up there. People want adults to sound like adults. They don't want adults to sound like kids. Men wouldn't find Frank Sinatra to be childish but they would easily find Bieber because of his high voice.
Elvis in the other has a baritone voice and his music was something different in it's time. Also, I heard that some delinquents liked Elvis music back in the 50s because it was louder and heavier than most of the mainstream stuff in that time.
People hated Frank Sinatra in the 40s and Elvis Presley in the 50s. However, Frank Sinatra kept a long legacy because his teen audience grow with him and his voice and face was considered really mature a decade later in the 50s. In fact, I was hearing a Elvis vs Frank thing and a Elvis teen fan girl said that Frank Sinatra is only a old man. Frank Sinatra was probably the most popular singer in the mid-late 40s and by the early 50s he had his own television show. His face and his voice was really mature in the 50s. Although, his voice was mature when he started. Frank Sinatra was something new and fresh because he was the first teen idol in music. Guys like Louis Armstrong and Paul Whiteman didn't had teen girls screaming at their music. Frank Sinatra was the first in music that actually had teen girls screaming at him. Then followed Elvis in the 50s and then The Beatles in the 60s.
Elvis was the first rockstar ever. Elvis was the guy who made rock and roll music to the mainstream. Elvis music wasn't really pop and it actually requires instruments and stuff. Elvis was also something fresh and new of course. The way how he shake and move his body surprised many people at the time. People thought it was inappropriate. Heck, Frank Sinatra hated Elvis and Rock and Roll music in the 50s. However, their friendship kind of grow in the following decade with Elvis and Sinatra performing together in 1960. Elvis and Frank were something new, Frank Sinatra was the first teen idol in music and Elvis was the first mainstream rock artist who brought the genre into the mainstream and made America and the worldwide world to listen to it.
Justin Bieber in the other hand will never have that type of legacy as Elvis and Frank's because he did nothing new to the music industry, his music is commercial pop music and his voice doesn't sound mature or manly. Just how many people actually remembers New Kids On The Block. They were a popular boy band from the 80s and new generation of people don't know who the heck are they. The new generation of people actually knows who is Elvis and also Sinatra. Most don't listen to it because they know those are old artists that aren't alive anymore. 20-30 years from now, the new generation of people are not going to know who Justin Bieber was because he did nothing new and was just another pop singer. I don't think Justin will never be up there with Elvis and Sinatra. Never.