Here's some information before we start;

I bought this bike for myself around Christmas, didn't know I'd be getting into road cycling at all.

So I bought a Mountain Bike for around 300$ (nothing too crazy) to ride and enjoy outdoors. I soon got hooked to long distances as I'm getting into road cycling. I exchanged my crappy stock tires with more slicker, road-type ones, and my bike can go 25mph easy for a MTB. Is it ok that I did this? It doesn't feel right but I love the distance, riding, etc.

What's your input?

I went through the same transition when I started riding regularly. As you keep riding distance and focus on efficiency a road bike will make a lot more sense. After I got my road bike I kept the MTB as a commuting bike until I gave it to a friend who got into cycling.

Plenty here have multiple bikes, as it sounds like you will in the not too distant future. In the meantime, just ride your MTB, save $$, and use the time to think about what features/equipment you want in a road bike. You could also test ride some road bikes in the meantime.

I could lie to you and tell you that you'll be content with road-biking your mountain bike, but in the end, you will succumb to the road bike. Keep enjoying your current setup. The heavier frame you are riding on will build up your strength and when you finally take the plunge into buying a road bike, you will be blown away at how light and fast it will be.

I'm looking forward to THAT! I, too, ride around on a $300 mtb, with it's original tires. I'm hoping to get my first new generation road bike in May. I say new generation because I had a Fuji 12-speed in college in the mid-90s, back when 12-speeds were still common and more than that was just becoming known.

I did the same thing as the OP with an Trek Navigator hybrid - took off the giant padded seat for a smaller one and put on some 1" Kendas. It made a big difference. And then my mtb was a step up from that, because though it was heavier it was more versatile. Now I'm ready for a real road bike and I can't wait to go FAST!

OP, as others say, I think it's fine to do what you're doing until you outgrow it, which will happen pretty fast. Start a bike savings envelope now!

This is funny to me. I had a mountain bike with slicks on. I really enjoyed it, used it for my daily commute for 4 or 5 years, beat the crap out of it on the roads. Never took it on trails, ever. I saved up for a year and a half, sold the mountain bike, got a much more "road"-worthy build on a cross frame. First weekend I had it? I went out off-roading through the woods. I'm dumb. I'm doing it all backwards.

I'm going keep my mtb because I do sometimes get to offroad.

^I'm starting to wish I had done the same.

How fast can it go with a rider on it?

I think it's fine for now. If you can afford $700-800, you will get a real blast from riding an entry level road bike.

If that's above your budget, ride what you have until you can get a road bike.

It's all good.