yes, as long as he reaches his milestones, he's fine.
actually from the time babies start to crawl, they'll seem to lose weight / fats cos they exercise (crawl/cruise/etc) more now. I see no concern at all.
and , dont't say drink breast milk halfway wants to play, since they are more mobile at this age, they may not be as interested in drinking milk, breast milk or fm.
my 2nd child also drinks breast milk less than my elder as a result, my supply is low this time. and even for night feeds, I have to supplement with FM. she's ok with that. She can sleep w/o drinking latching on too.
my elder was on breast milk til 3 years old and started on formula only at 2 years old. no issue on the transition too.
I'd say, if you can, give breast milk for as long as possible.
recently, my whole family kena a super strong virus and only my daughter who is still on my breast milk was spared. Thanx to the antibodies!
This really encouraged me to carry on breastfeeding cos I was considering to give up since my supply is super low now.