Old (late 40s) first-timer struggling to make progress...

I'm hoping some of my fellow geezers can lend some advice. I've ridden bikes my whole life, but I've never "done BMX" -- like, tricks and whatnot. I got a used Fit PRK about 8 months ago as fun a way to stay in shape. My cardio is OK and I don't have too much extra weight, but I'm also kinda weak I think.

I've managed to bunny hop pretty quickly, but I still struggle to manual and my bunny hops still haven't gotten any higher than about 3-4 inches. My goals right now are to be able to do box grinds and 180 on the small quarter pipe at my local park. But I can't even hop high enough to grind yet.

Am I unreasonable to think I should have made more progress by now? I've really only been able to go out once a week for 30 minutes each. I can probably add one or two more sessions a week if I knew it would help but right now I'm feeling very discouraged.

Also, is riding enough for me to build the strength I need to do grinds and 180s? If not, do you have any exercise recommendations that don't involve a gym or weights?

Thanks!