Knee feeling after long ride with road bike During the last 2 months, I rode on my road bike for a few times (about 7 times) a way that is about 60 km (37.282 mi) long. Two days before, when I did this ride, after the midst of it, I started to fill very comfortable regarding the effort that I needed to put on pedaling, even though I started to pedal on the harder gear speed. Almost the hardest on my bike. The ride was beautiful and amazing, I did it in a very good time. Now comes the problem - I don't really think it's a problem, but I want to meet any possible bad thing that can happen if I can do this.
After I rode, my feet feel a kind of weary, but especially my knees. It's not pain. I'm just weary on my knees. When I sit on chair or bad (before to sleep), I feel very comfortable with my knees, it's a sensation of total relaxing on my knees. I have to underline that I'm not very trained, and this is the majority of time in the last two months that I spent on my bike. Before, I rode only on my little town with my city bike.

I'm interested if anyone experienced this before, and if this is due to the lack of train mostly or if it's due to bad saddle fit. Any other possible issues?

N.B. I know I must check for saddle position. Actually I'm searching for the best fit that I can have, but because in my town I don't have a specialist in this area, I have to document myself for getting the best fit.
If you ride further or faster than you're used to, then some weariness in the legs is normal and should pass within a couple of days. I rode my biggest ride to date a couple of weeks ago and when I got home I nearly lost my balance walking around the house as my legs were a bit weaker than I expected. With a couple of days rest they were back to normal, however.

Besides rest, what can help your recovery is static stretching (not bouncing or bobbing). Here are some suggestions for knee stretches. 

As others have suggested, a higher cadence (therefore a lower gear) may help, even if you can't measure it precisely. I have a knee injury from running, so I change down a gear the moment it gets uncomfortable.

For bike fit, trial and error can work well, here's a link to some simple bike-fit tips which may help you move in the right direction.

All that said, if discomfort becomes pain you should obviously stop doing what hurts and get advice from a physio, ideally one with cycling expertise.