I'm 31F. I was very active and strong as a kid (I even had a four pack at 12 lol) but lost confidence in my body after middle school and I've been sedentary since. I also have back and glute pain from (mild-mod) scoliosis.
I've tried to get started a few times over the last 15 years, joining gyms or starting home routines. I finally went to a personal trainer for like 7 months, going 2-3 times a week. I went up a couple lbs in weights (minimal, like 5 lbs to 8 lbs) but otherwise felt no different. I had to stop because it got too expensive and I didn't continue on my own because I was discouraged from lack of progress. I also developed knee pain (I think from bad form doing squats and lunges).
I especially want to strengthen my core, back, and glutes because I worry about my back pain worsening as I age. But most beginner core exercises I do just hurt my back because I can't even figure out how to engage my core properly. I also don't know how to engage my glutes.
In an ideal world I'd love to be visibly muscular but I feel like that's a pipe dream. At this point I just want to not be totally out of shape. I'm thin so I'm not looking to lose weight, I just want to be able to engage my muscles properly, challenge myself without hurting myself, and keep up with it. I feel like I'm running out of time.