First of all, welcome to the forum and congratulations on getting into cycling. I'm in your age range as are several others here. I'm an experience cyclist, getting back into it after a break of several years. The issue of drop bars vs. upright bars is a sticky one, but not insurmountable. Not to be discouraging, but because you need to know, here are some things to consider. 1. Drop bars, regardless of the height at which they are mounted (relative to the seat height), are better. I say because they offer 3 times as many hand positions as flat, mountain-style bars, or as swept-back, cruiser style bars. I recently went through the process of converting my road bike to flat bars, and soon decided to go back to the drop bars. Your hands will get more fatigued and sore if you don't have the ability to switch positions. Modern road brake-shift levers (aka Shimano STI, for example) offer a very comfortable primary position for your hands on top of the hoods. You also have the options of riding more upright with your hands on flat center portion of the bars, or down in the drops. These three positions vary the angle of your wrists, and this is a good thing. 2. With a proper stem, you can raise the drop bars up to a level that is comfortable for many (I'd say most) riders. If you have back problems and need to sit perfectly upright, that would be the exception. 3. The bad news is that modern, mass-produced, quality bikes are now made with "threadless" forks, which dictates a type of stem system that offers less hight adjustment than older "threaded" forks. I won't go into the detail here, but there are some options for raising the stem on a threadless system, and they may be sufficient to get it a good height for you. 4. Yes, a drop-bar bike can be converted to upright bars, and vice versa. However (and I've just gone through this myself a few times), you have to change the brake/shift levers, bars, and possibly the stem. You have to be mindful of the type of brakes on your bike and whether the brake levers are compatible; also true for the shift lever functions. Many would tell you that you should just buy the type of bike you need with the bars you want, but that's difficult if you haven't ridden much. If you start with flat bars, you may eventually (or in a short time), wish for drop bars. So I don't have any easy solution for this question. Your LBS will, of course be happy to sell you a bike and convert it later, if you're willing to pay.
I'll stop for now, and see what others suggest. Good luck, Steve