C2-C3 means that he is singing a 5th above and a 4th below F2 - which is about the usual range in the key of F
C2-C3, is only an octave, Most singers have an octave and 4th or an octave and a 5th as their range. Moving on to those with trained voices some get two octaves or even three, by using falsetto/head voice as well as chest voice. What Valentino hasn't said is whether this is a supported voice (chest voice) or a throat voice, which is actually going to damage his vocal chords (think nodules on the vocal chords a benign form of cancer that can metastasise into malignant cancer if not treated) or a head voice.
With a bit of work, I am sure that Valentino can actually get to F3 no problems
In G C2 is a fifth below and C3 is a 4th above, reverse of F
Depending on the song, Cmajor/aminor may work.
As for other keys, difficult to tell.
Gb/F# major/EbD# minor is possible, as is E major/C#minor but it would be stretching it.