Worried about my pastel bp's size/weight

[Deadringer21]

[Edit] Yikes...Sorry in advance for the length of this post. tl;dr do these pictures look like a one-year old ball python? [/Edit]

What's up ball-pythons.net? I've been lurking around these parts for a couple of months, but I just now decided to register in hopes that I can get some advice regarding my concern for my new pet's development. I got Braska, my pastel ball python, from a PetSmart location in the middle of this past March; the girl who helped me with the purchase told me that they'd had him (or her? who knows - I'm not too worried about it) since June of 2015 (about nine months) and that their snakes are generally around three months old when they get them in, so we estimated that Braska was about twelve months old at the time. I didn't learn that they'd had him for nine months until just before the check-out process, but once I heard this I was shocked at how small the little guy was (pictures at the end). I didn't really measure him in any precise way since I didn't want to disturb him too much right off the bat, but I'd estimated that he was about 22-24 inches in length. A week after I got him, I clocked his first weigh-in at 80 grams on the nose. I was really expecting him to be much bigger than this (or really, I suspected that he was younger than I was told), but they gave me some paperwork with his feeding schedule which shows that they'd definitely had him for as long as I was told.

Anyway, since I got him I've been feeding him on a weekly basis, and it seems like he's been doing very well in his new tank in my living room. With my once-a-week feeding routine, he's yet to deny any of the meals I've offered him. Let me break down some of the details in a quick list:

• First of all, I noticed when flipping through PetSmart's feeding chart that they had him for exactly 38 weeks and offered him a meal once a week (every Thursday). Upon going through these records, I found it to be very concerning that he'd only taken a meal during 16 of the 38 offerings, including an eight-week period during which he did not eat... (spanning from 08/27/15 until he finally took a single f/t fuzzy on 10/22/15)
  
  • His last four Thursdays at the store show that he: ate two fuzzies, declined to eat, ate two fuzzies, and again declined to eat, respectively. These two double-downs are the only times he took two fuzzies; every other time he at, it was just one (and I'm not sure when they started offering two fuzzies per feed)
  
  
• I picked him up on a Wednesday, and the girl I worked with told me that he'd just finished shedding and that it probably wasn't even worth offering him a meal the next day since he'd be stressed from the move into his new home. Well I figured it was worth the $1.25 fuzzy charge just to try it out, and he did take the meal (his first kill!). Following this meal, I left him alone until the following week which was when I first weighed him
• From here, I began to stray from the routine Thursday feedings, though I am still keeping to an offering every 7-10 days. The following week I decided to give him a small mouse (a bit larger than a hopper) and he made a beautiful kill and willingly took the meal (I felt it was worth giving him something a bit bigger since he's a year old ball python)
• Seven days later, I fed him another small mouse which he took just as gracefully as the previous week's meal. Unfortunately, he ended up regurgitating the mouse two days later I felt terrible since I know this is a very stressful experience for a snake, so after I thoroughly cleaned out the tank I left him to relax for a week. Seven days after this, I started again with a two-hopper weekly routine
  
  • I believe he regurgitated this mouse simply because it was too big for him; I've been maintaining his tank since day one at about 60% humidity with the cool side being 78-80F and the hot side being 87-90F - he has a hide on each side with a large water bowl in the middle
  
  
• Since I picked up the two-hopper weekly routine, he's been eating at every offering and has not had any subsequent regurgitations

Ugh, is anyone still reading after all of that? Sorry to babble on in so much detail, but I figure more is better than less. Now, in less detail, I'll just include a very quick summary of his eating and his weight since I got him:

• Wed 3/23 - Braska came home with me
• Thurs 3/24 - 1/1 Fuzzy
• Thurs 3/31 - 80.0g
• Sat 4/2 - 1/1 small mouse
• Sat 4/9 - 1/1 small mouse
• Mon 4/11 - regurgitated above mouse
• Mon 4/18 - 84.9g (before feeding), 2/2 hopper
• Mon 4/25 - 92.6g (before feeding), 2/2 hopper
• Tues 5/3 - 102.5g (before feeding), 1/1 extra small mouse (slightly bigger than a hopper, whereas the previous small mice were a fair amount bigger than this one)

So anyway, that's my story and I'm stickin' to it. Now, I don't know a whole lot about snakes (besides the extensive research I've done for this guy's tank and such), so I feel slightly stoopid for asking, but...he is a ball python...right? I mean at this point he's just about 14 months old, and he weighs a measly 102.5 grams as of yesterday. I've done lots of searching for some kind of standard growth-rate chart, and everything I've found shows ball pythons to weigh around 400g by eight months or so. I know that each snake will vary with its size and weight, but this difference seems WAY too huge to ignore.

It is concerning, but on the plus side I'm finding comfort in the fact that his weight is up exactly 20% since I started feeding him again after the regurgitation (16 days ago). 20% in 16 days, to me, suggests that he seems to be getting into a healthy growth rate since he's gained 10% mass each week. Further, I find it comforting that he's yet to refuse a meal since I've taken him into my care.

My main theory is that he was probably unhappy in his enclosure at PetSmart; a little guy like this should surely be eating MUCH more often than 16 times in 38 feedings (as he is now that he's with me). Also, he had just been finishing up a shed cycle when I got him, and still he has areas around his neck and head where the skin hasn't cleanly come off. Again, this brings my theory to include that the PetSmart probably didn't maintain anywhere close to proper humidity or even adequate tank sizing (the tank seemed to be a 10-gal tank, cube-shaped, which had an overhead light with a screen-top).

Here are two pictures I have of him from the first time I took him out to "play" about a week after I got him. Again, he's about 12 months old at this point. I don't have any full pictures of his tank right now nor can I take one since I'm currently at my office, but I can attach that as a follow-up if that would be helpful. My main question here is whether anyone has ever heard of a year old ball being this small... So for now I'll turn it over to you wonderful people; any comments and constructive criticism on what I've said above are welcome. Thanks in advance!