4mo is on schedule for a growth spurt, no? I remember DS guzzling down bottles at that age - a friend still recalls with a certain disturbed tone the time that he downed 12oz in front of her in a cafe 
It happened once, it was just a phase and disappeared almost as soon as it arrived.
Yy to 4mo often grabbing anything, DS kept going for our cups, plates, forks, food, and equally phones, remotes, books, jewellery... he still does at 9mo 
There was a marked difference at 5mo, when he started to get very agitated during mealtimes. He displayed all of the signs of readiness (checked on MN pages!) and eventually it got too much as he was really starting to lose it whilst we ate and did actually manage once to grab some pastry and practically inhaled it 
So at 24 weeks (ie 2 weeks earlier than 6mo), we started giving him some steamed veg whilst we ate our main meal, following BLW. He ate very little, if anything at all, but it made him happy and kept the peace, and it seemed counterproductive to do differently. But I felt confident as he displayed all of the signs, he was close to 6mo, and I only offered food that was okay for under 6mo (again, MN weaning pages came in handy!). Largely, things like broccoli florets that he mainly gummed a little and then was done.