While it's challenging to significantly alter the sound of your voice without using any external devices or software, there are some techniques you can try to create the impression of an older man's voice. Here are a few suggestions:
Adjust your vocal pitch: Older individuals often have lower-pitched voices. Try consciously lowering the pitch of your voice by speaking from your chest rather than your throat. Practice speaking in a deeper, resonant tone to emulate an older man's voice.
Slow down your speech: Older individuals tend to speak at a slower pace compared to younger people. Slowing down your speech can lend an impression of maturity and age.
Use deliberate speech patterns: Older individuals may enunciate more clearly and emphasize certain words or phrases. Pay attention to your articulation and consider adopting a more deliberate speaking style.
Introduce vocal quirks: Some older people have distinct vocal characteristics, such as a slight tremor, a rasp, or a more gravelly quality to their voice. Experiment with adding subtle quirks to your voice to create a sense of age.
Modify your resonance: Older voices often have a more resonant quality. You can try to achieve this by imagining your voice vibrating in your chest or nasal cavity while speaking.
Remember that these techniques may only create a temporary effect and might not result in a perfect replication of an older man's voice. If you require a more consistent and accurate transformation, consider using voice modulation software or professional voice-changing devices, which can provide more precise control over your voice's characteristics.