What loft was he using on those heads? The Flash is a low spin head, I forget what the TS2 is. With an 85 mph clubhead speed I’d be as concerned about the head as I am the shaft. The Flash also has the weights, how are those set up?
FWIW my son is also small... older than your son but he is 5’even and 80lbs. He hits a Ping G SFT 12 degree with a senior shaft. Hits it about 225 yards with a tight little draw. He has always had a draw anyway.
I didn’t mind getting him the SFT because he plays it at full length and the SFT feature would enable him hitting a draw with a shaft that’s too long so he would get some distance.
So I haven't been pleased with my putting lately. It just seems like I have been fighting it on the backswing, and that is throwing me off.
So I thought I would pull out a bunch of putters. like many people have and weigh them and see what the balance turned out to be. This is not scientific since I am using a Taylormade Monza IB Spider as the baseline weight and using a digital scale. I realize this only gives me overall static weight of the putter and not the head weight. I'm just guessing at that since they all have small pistol grips. The IB weighed 537gr and has a spec of 350gr headweight. It has a slight toe balance.
1930's Burke 15oz, 90* toe balance (Found in my parent's garage as a kid and actually used it a long time ago because I thought it was cool).
1985 Taylormade TPA V 488gr 17-1/4oz, guess 300gr HW slight toe (First real putter that I used for a long time... Nevada Bob's).
1990's Teradrops TD-xx 504/508 17-3/4oz, guess 315/320gr HW slight toe (Drank the roll face kool-aid a few years ago, they do roll nice).
2008 Adams Mallet 523gr 18-1/2oz, guess 335gr HW face balance (Got this after wife took my IB, I loved this putter before Jim Jones got a hold of me... back in the bag).
I have others, the 80's are around the same weight (slight toe, except one that is about 80*) and I have a Teardrop RFD that is "toe up" by 30* and is almost 19-1/2oz-360gr HW. It is super stable... but boy I hate that one.
I realize that my list is really low budget and most people wouldn't be caught dead with any of them. But this was kind of an exercise in looking back at the years and also have some baseline for me. I don't buy a lot, but I realize that I've picked up too much of the same that isn't working, at least for my current setup.