There's no need to apologize for being a teenager and having a lot to learn.
Ironically enough, in this case I think you would benefit from thinking less and "doing" more.
It's good to evaluate your technique and try to make sure that you're using "good form" but that can go too far. When someone that can already deadlift 225 feels the need to literally pause in the middle of a rep at 135 to turn sideways and look at themselves in the mirror - which, as explained, is entirely disruptive to the technique you should be using in a deadlift anyways - that's a surefire sign of too much thinking.
I've expressed this opinion elsewhere, but I think form videos taken with less than about 70-80% of 1RM are mostly pointless. Your technique looks different with weights in a working range near your max than it does with warmup weights; watching someone deadlift 135 tells me basically nothing about how they'll look at 405.
To address a few of your other concerns - yes, it is possible that different equipment (bar, plates, whatever) can have a slight influence on what you can lift and how it feels. I changed gyms earlier this year because I realized that the CrossFit box near my place had much nicer barbells and plates than the regular commercial gym I'd been lifting at; now I'm about three weeks from moving into a house of my own and outfitting a garage gym, and I'll be getting some good stuff to make sure that's not a concern. But that's not an excuse for shitty form on your lifts - do the best you can with the setup available to you, and then when you transition to better equipment, that will be reflected in your numbers.
- more doing, less thinking. It's fine to keep checking in on your technique, but if you keep posting 135 form videos, you're basically just spinning your wheels.
- read the tips given above about breathing and bracing, and keeping the bar close to your shins during the pull (you don't need to exaggerate this, but the bar should be in contact with your legs most of the way up). You'll be given this advice every single time you come back here to ask about your deadlift form.
- if you ever post a video of yourself looking in the side mirror before/during a deadlift again, don't bother coming back here