This is a decent demo. It's short, sweet, and to the point on what you can do.
HOWEVER
The first voice felt really weird. The delivery felt a bit forced and the aging of your voice needs to be a whole not more stronger if you're gonna do an old man voice. Whether it being exaggerrated or realistic, doesn't matter. Age your voice up, and put more energy into it. Most of all, projection is everything with both voice acting and acting. In other words, be a bit louder when you do certain voices. In the case for your old man voice, keep the same volume more or less, but put more shake and possibly even replicate vocal nuances in an elderly man's sound.
Shake your voice up when trying to sound old, it sounds way better when you do that. Especially when exaggerating it.
The second voice definitely needs more energy, and feels too close to your normal voice that you show in the beginning. And you are way too quiet, and the tone of your voice really doesn't fit the background music that you chose, making that portion have a whole lot less impact. Don't be afraid to get loud, or get energetic vocally for characters. Cause it feels like you're holding back your voice almost.
Third voice is really great. I absolutely love it. It's a really chilling, yet beautifully performed portion of the demo, and shows off your dramatic voice acting damn well. So already in this demo, I can tell your better for dramatic voice work than you are comedic. That ain't a bad thing, but it won't hurt to practice comedic voice acting for more versatility in your voice acting. Your dark, deep monologue on the third voice really is nailed brilliantly. It's a really good voice for dark monologues or noir narration. Good stuff, dude!
Now your fourth voice feels really forced. This one really needed more loudness from you. More power from the diaphragm. And making use of all the gravel from your throat is important when doing a demon voice. At first, I legit thought it was supposed to be an orc, and it confused me. Because you're doing a demon, don't be afraid to perform some demonic laughter, or really just bring out the most fucked up voice you can muster. There's more to voicing a demon than just clenching your adam's apple. Practice it intensely. Study up on demon voices from the new Doom, and keep it up. You have potential and it shows here.
I could probably one day use you for a dark monologue cause you're fantastic at that. You're good at bringing your voice lower (not super low, but low while not being forced or cringy with your vocal range). Voice acting is a lot like art. You keep practicing, and you are one step closer to perfection.
It took me freakin forever to get it "just right" for me, and finding a comfortable place for my voice, but I hope you pick it up quicker than I did! Good luck, my dude.