'mature voice' is correct and usable in written English.
It is used to refer to someone speaking in an authoritative, measured, and experienced manner. For example: "The politician delivered a powerful address in a confident and mature voice."
In her teens, her prematurely mature voice won her a talent contest in Marseille.
As Marke, Matti Salminen, his mature voice sometimes hoarse, befitting the part, performed magnificently.
Not until "The Counterlife", in 1986, did he find his more mature voice.
Like Sappho, she found, in her mature voice, a complete swift trust in the image to say everything and anything.
Bundle proved a standout act with his polished and serious performance, showcasing his mature voice and the song's resonating lyrics.
Although it lacks the color of a mature voice, it is bolstered by good pitch, broad range and considerable strength.
They were singing with such mature voices, like men of 50 or 60 years".
Contrary to custom the material chosen demanded big, mature voices and had a cast of only three.
With its 900-seat theater, Glimmerglass has been a place for young artists to take on major roles that would require big, mature voices in a full-size house.
Works by Al Held and Frank Stella, both of whom felt compelled to impose geometrical regularity on the forceful gestures of Abstract Expressionism to find their own mature voices, suggest as much, as does that of Valerie Jaudon, whose art was in turn influenced by Mr. Stella's.
Moreover, the alleged more mature voices within the Republican Party who have stood by and said nothing while this all occurred are clearly unwilling or unable to moderate what could charitably be described as the angry, unhinged mob formerly known as the Republican base.
