I got an A* at GCSE this year, and I'm currently working my way through C1.
You could definitely do A Level maths if you really wanted to. In the week or so before school starts, my best advice is to pretend you're redoing your maths GCSE. If you're able to get an A* in GCSE exams, you're ready for A Level. If you're either too lazy or otherwise unable to achieve an A* at GCSE, I wouldn't recommend taking A Level maths. This is because C1 starts at an A* GCSE grade, so you'll essentially be two grades behind right from the start.
In short: if you can get an A* at GCSE, do A Level. If you can't, don't.