The seams are basically where new scutes/bone are growing. As it matures, the color will change back to normal, and you'll see new growth seams form. This will happen long before any shedding.
The danger of it happening too fast is that the old scutes won't shed off fast enough as new ones come in. This can lead to what is called pyramiding--instead of a smooth shell, there will be pyramids of retained scutes. The scutes are a protective layer of dead tissue, think finger nails or hair. Since it is layers of dead tissue, there is no immune system operating. Pyramided scutes can lead to a greater chance of infection, that can grow protected underneath the layers of retained scutes. This infection can spread into living tissue. Worse, since it is a big healthy infection once it hits living tissue, it can overwhelm the ability to fight it off.
It's not guaranteed that will happen, but multiple layers of unshed scutes ups the possibility.
Don't panic, though. You don't have multiple layers yet, and many of us did the same things with younger turtles. Search some of my posts and you can see pictures of my turtle with growth seams and concern that I was over feeding. Many of us have been there.
If you don't cut back on feeding, you may have issues down the road. If you do, you may have an extra layer or two of retained scutes that will eventually be shed away.
I don't know how accurate it is, but one comment I read as I was struggling with this was to look at the area between the front legs and the neck as your turtle is swimming (the equivalent of just above the collarbone on us). If it bulges out, you are over feeding. If it goes way in, you are under feeding. If it is smooth or better slightly concave, you are doing it right.
I can tell you that it is difficult to get it right with a turtle your size, from, my experience. It's like even feeding the same amount can be fine for a while, then it's too much and the growth seams are back, then they've grown so much that the pellets you are always feeding aren't enough.
In the wild, your turtle would not get such regular food. You'll realize if you are under feeding. And, even if you over feed, your turtle will beg for more and act like its starving any time you come by. At least if mine is any guide.
Here was my post concerned about over feeding:
viewtopic.php?f=8&t=33092You can see from the picture the same yellow edges and growth seams that were almost as bad, though you can also see them starting to turn into scutes with color.
I did cut back at that point, and his shell looks much better now.
