i want to make tutorials on youtube, but i sound like a kid and i want to sound like more of a man. so is there a way to make my voice deeper, and if possible, change in real time? sorry if i have bad grammar, english is not my first languages.
If you are unsatisfied with Audacity's ability to manipulate the voice, then the best software I can recommend where you can customize its capabilities are Csound, Max/MSP, and Kyma X.
However, if pitch and formant shift isn't working for you, may I recommend a radio talk host approach?
Get yourself a great microphone, for e.g. the ones used popularly in radio stations like EV RE20, and get sound dampening foams to assist in concentrating your voice. This should help to retain your vocal frequencies, specifically the mid and lower ranges. I hope you don't misunderstand my recommendation as a $500 - $1000 price tag of professional studio gear, but as a way to rethink your problem.
With that approach, applying some eq and compression will go a long way.
This will not only enhance your natural voice, but will make you feel confident. The deeper issue isn't about trying to sound deeper and older, but to be comfortable with your voice and mannerisms.
Pitch shifting is the effect you want to use, and this can be done either with a pitch shifter application, or by stretching your waveform.
It will reduce the pitch, but this may not make you sound older, just different, as adult voices typically have different resonances etc. Have a play with it anyway and see what you think.
In Audacity, to change pitch directly, use the
Effect > Audacity > Change Pitch selection and you can decide how much up or down you want the pitch shifted.
Effect > Audacity > Change Speed stretches (or shrinks) the waveform this lowering pitch and also increasing the length of your sample. For YouTube voiceovers, this is probably not what you want, as it will throw off your timings.