There's always a first time for everything, right? Going to the gym for the first time is going to seem kind of overwhelming. When I went to the gym for the first time I felt like everyone was judging me. Of course, nobody was actually doing that. Everyone there was once in the exact same position you were now in. They completely respect you.
The reality is that EVERYBODY at the gym is there because they are trying to lose weight or build muscle or simply wanting to stay healthy. Most of them are just as self-conscious as you are! We all have insecurities about our bodies, no matter how mature we are. Don't let your initial anxiety and insecurities stop you from being active or achieving your goals. Don't compare yourself with others, and never try to look like someone else. Your DNA and body type are unique to you, so celebrate that.
No matter what your weight, gender, or age is, you've made a decision and you've shown the fortitude to put that decision into action. My advice is: keep on showing up, say hi to people, ask questions, and pretty soon you'll be a familiar face at the gym whom everyone knows and appreciates. Find a gym that fits your fitness goals, give yourself time to orient yourself to the place, and soon enough you'll have a full-fledged workout routine. And in the end, just know that you are always your own worst critic. Others don't really care about how much you're lifting, so be confident in yourself. What's most important is that you find a way to move your body that is fun and achievable for you.
There's more we could explore on this subject. Let me know if you want a follow up!