Adult Newbie Wrestler Struggling With Level Change / Penetration Step

I'm an adult beginner and I'm really struggling with the basics. I get the theory behind changing levels and doing a penetration step, but I'm always either not stepping deep enough, or I'm not changing levels properly. I either end up bending at the hip and basically zombie-ing forward, head down, reaching with my arms, or I'll drop and get the knee down but then not have the power to really step back up explosively, if that makes any sense?

I'm guessing I'm tight somewhere, or lacking strength somewhere (I'm in my 30s and had a desk job for ages, I do BJJ as my main sport now so I'm not 'unfit', but I'm not wrestler fit either).

Is this a common problem? Could anyone recommend some drills that can help with the footwork, please, or something that I could do to fix how generally stiff and awkward I feel when I'm trying to do the level change?

My coach has me shooting against the cage wall to get me keeping my head up, but as soon as I'm shooting at someone instead of the air, my takedown attempts just feel really weak.

Thanks.