To me, glamorous is about being a bit extra, looking fab, perhaps deliberately going for an artificial look, sparkly and so on, so anyone can be glamorous but very very few people are in real life (the red carpet aims for everyone mostly to look glamorous).
I would rather be glamorous than elegant but that's just me. I don't want to be Audrey Hepburn when I could be Sofia Loren! Of course I look like neither, I'm a middle-aged slightly overweight lady with a round middle. Things I do that make me feel glamorous is wear the odd top lower cut than most, usually have one tight thing on (so tights, tighter trousers, possibly tight top but usually something covering the middle bit). I wear the odd heel if I'm off out (not too high now they aren't so in fashion). Make-up, jewellery, sparkly things, blazers. I don't want to look stylish or elegant or discrete or boring, I would hate to look like Kate Middleton as it's not me. I would love to be described as glamorous, and can occasionally rise to the occasion, but these days it's all a bit hard work.
I think you can dip in and out of being glamorous, so Lizzo definitely is glamorous but not all the time. Sportswear is never glamorous even though it looks great.
Glamour isn't size related for the most part, only if you don't feel confident in yourself you will find it hard to be glamorous (it also attracts attention).