The yellowing cotyledon leaves are nothing to worry about. They don't really photosynthesize so all they do is store nutrients for germination and sprouting. They usually die off once the plant has consumed all of their stored goodies. You're fine on that account. Is this day 16 from sprout or day 16 from planting? What kind of soil is that? It might be running a little hot as there is some slight yellowing on your first true leaves. Lights might also be a bit close. Looks like there might be some burn on the outside of the leaves. What is your current setup, and do you have a fan on them? All in all, they look pretty okay, man. Your stalks are pretty thick and color isn't all that bad.
I only have one plant 'Blue Mystic auto' I got, it's m first one and its in a computer case there are two fans and one extracting fan all are computer fans and I have one 23w cfl spiral bulb 1300 lumens
It's in a ziplock bag ATM because its humidity is very low should I take it out of the bag or leave it in? Also when should I think of transplanting to a new bigger pot?
Okay, heat from the light isn't an issue. You're okay with one 23w for now but you'll need to add a lot more light if you want to produce much. If it's 16 days from breaking soil, the slow growth could be from a lack of light. Here's a picture of one of my plants at 14 days old. Here's another at 8 days. Do you know what temperature the bulb is? (2700K or 6500K) EDIT: Any idea what your humidity is? When I started my humidities were below 20% and it didn't negatively affect my grow at all. The bag isn't all that necessary once your plants roots have adequately developed. Also you really don't need to transplant for a little while. Didn't transplant mine until day 25, but with an autoflower you should transplant to your final pot soon. They tend to not respond to transplantation very well.