I was basically the exact same guy. My teen years and the entirety of my 20's were spent drinking, getting high, playing video games, watching movies and just generally sitting on my ass. Then not long after I hit that 3-0 I had an epiphany of sorts. I realized I should be in the prime of my life. I realized I should be in much better shape. Instead I felt like I was 50 and yet I had the body of a teenage video game addict.
That was over 3 years ago. And I made a ton of mistakes early on which I regret. But now I'm finally happy with my body and believe I look much better than most men my age. I'm not "swole" but I look and feel good. And I honestly never thought I'd even be able to get to this point.
It's not too late for you. Here's the way I looked at it. If I can't kick myself into gear in my 30's I highly doubt I'm going to do it in my 40's or 50's. I actually think this is an ideal time to get your health back on track. You had your fun in your teens and 20's. Now set new, healthier, sustainable habits that will improve your life on into your 40's, 50's and beyond.
Few tips as a fellow "started in my 30's guy":
1- Be patient. This is so important. Beginners often have unrealistic expectations as to what they can achieve in X amount of time. Then when that doesn't happen they get discouraged. Consistency+Time is the key.
2- Don't overthink things. E.G. "Best routine", "optimal reps/sets", "HIIT vs. LISS". None of that stuff matters much. Particularly when you are just starting out.
3- Don't compare your progress to folks you see online. That progress post you saw where the super skinny 17yo kid got jacked in a year? Sorry, but that's not your situation. As an "older" (relative term) lifter, progress may come slower for you. But that's okay. Remember, you are trying to be the best version of you. Not beat out some random stranger on the internet. Also, a lot of people online are simply full of shit anyway.
As for your actual question, stamina will come with time. You are still very new at this. As for being stiff, look up some mobility drills. Look into yoga. Pick literally any beginner routine in the wiki that will realistically fit your schedule. If you don't know what a particular lift is, google and youtube are your friends. There's literally no question you could have that you can't find an answer to.
Good luck.