You are losing all tightness into the bottom and exhaling early. More importantly, your back angle is too vertical on the descent. So:
1) Bend over early. Maybe warm up with a box since you are uncoached. This will force you to bend over and reach back.
2) Slow the tempo down to eliminate that relaxation at the bottom.
Fixing these things alone will help you move along.
How the heck did you catch that I lose tightness at the bottom? You've got freak'n X-ray vision!
I am guessing that I do that to help reach parallel. I'm sure I'm not the only lifter who started at my age that has difficulty reaching parallel.
I will do my best to implement your advice, and keep you posted. THANKS!