Honestly, if that is your attitude, Don't become a volunteer. Yes, it will be hard to volunteer while you are working another paid job, but it is what lots of us needed to do to get our foot in the door. Most places will not hire you until you are 21 (some 20.5). In my experience, private agencies (the ones who are more likely to have jobs available) do not do a great job of training- my training was only 6 days long, and it terrifies me that someone brand new to EMS can come into my agency, have 6 days of training, and then be released as a provider. I volunteered for a year before I got a paid job (I also was not old enough), and I am so grateful for my experience volunteering. I had mentors who wanted to teach me and make me a better provider. Had I not had prior EMS experience, I WOULD NOT be comfortable now being an EMT, after such a short amount field training. But as I said, the private agencies are looking at the bottom line. They need more providers and do not want to pay for a longer field training time when you are only the 3rd person on the ambulance instead of clearing you to practice as a basic.
IMO, you need to look at why you really want to do this. Are you in EMS simply for an 'easy' job and money? If so, get out now. Hate to be the one to break it to you, but you will never make 'good' money in EMS. However if you are in it for your love of EMS, then it won't be to much of a burden to volunteer first, while you build up your experience and wait till you get a little older to be hirable in most places. +medic mentioned IFT BLS trucks. That is another option job wise, if they would hire someone your age, but I know multiple people working IFT who also volunteer in a 911 system, just for more experience, and again, to make those connections that will be useful when you are looking for a different job.
Long story short: yes, it will be hard work, but it is what you make of it. Your time spent volunteering should not suck, you should look at it as an opportunity to grow as an EMT, and be making a great impression on all you interact with so they can think "wow, I really want EMTDavid to work for us". Make those impressions and gain experience now, and in a few years, you shouldn't have any trouble finding a paid EMS job.