Hi Bryn,
Welcome to the forum.
Don't get frustrated... as with any skill (and
VO is skill) it just takes practice.
I do have to disagree on the time frame for a demo. It's really an individual thing. Some people are ready to work immediately, because they're 'naturals.' Others need more training. One big key is PRACTICE in what you learn.
Get a good, trustworthy coach, who cares more about YOU than your money... and let them help guide you into when you're ready for a demo. Basically, you're ready for a demo when you are good enough at
VO to land work. That doesn't mean you're not ready for demo till you're ready to land national work or a Los Angeles agent. But tht you can at least start making some money immediately, like on bottom feeder jobs at voice123 or better jobs at voices.com. Then you can have a little income to at least help pay for your training,and more importantly...to make you a "professional" so you can write off your training on taxes as professional development.
One student I had was ready immediately, full time
VO within two years, and now works regularly on Discovery Channel, DIY, and other networks. I had another student who came for a demo session, and I coudn't do it because he just wasn't ready.
So, find a coach with integrity and a conscience, who will guide you based on what is best for you!