Gaining

Hard to say from these pics, but I guess so. Stretchmarks look as if the skin has burst open along a line and the skin between the borders is a little deeper and uneven (not as smooth as skin usually is).



A bit like this:

I have a few on the inside of my thighs, and they didn't even come from gaining quickly. I was not even overweight. I noticed them only some time later. But I remember, when I was 15 or 16, there was a hot day, and I wore a jeans skirt, so my legs kinda glued together while walking. It hurt, but I didn't think that this would have any other effects. But obviously this was enough to stretch the skin too much.

Here stretchmarks are called pregnancy stripes btw. A term meaning stretchmarks exists too, but it's less used.

Basically stretchmarks are caused by stretching the skin too much. You get them easier if you have a weakness of the connective tissue. Hormones can also reduce the elasticity of the skin. But in the end stretchmarks are scars.

Lovely.

You can find creams against stretchmarks, either to prevent them (there's no proof that they do) or to alleviate them (they don't work), but you certainly won't find any in order to damage the skin. If you want to inflict stretchmarks from outside, all you can try is to stretch the skin mechanically. But I doubt that this will work just by pulling your skin away with the hands.

People pay a lot of money for creams and surgery to remove stretchmarks. It's kind of funny that someone would like to get them. But it's the same with cellulite. Maybe there are also people who can't wait to get wrinkles or lose their head hair?

Cellulite is mainly a female thing. The connective tissue of men is usually closer meshed, so fat cells are kept below it. In women enlarged fat cells can push through it, which gives the skin the dimpled look.
If you don't have a predisposition for cellulite, you won't get it or only at a higher weight. I have a hard time to figure your body out in your pictures, but you don't look that big. Where should the cellulite come from? There is no advice anybody can give you.