Mines like this. He's an infant still but he sleeps like that in his crib and in his sleep sack
my son sleeps like this, my husband's best friend is 35 and still sleeps like this
My LB 29m and sleeps like this although wears a sleeping bag with feet.
I've heard multiple things about this position (mine also sleeps like this). One is that they're cold but my boy never is. Another is that there is an airway issue (I actually suspect this with mine). And the other is that it's just comfy and they like it! If she doesn't feel cold on her chest and is rejecting a blanket she won't be cold.
My daughter is 2.5 and still likes to sleep like this regardless of other factors.
My 18 month old sleeps in this position all night every night I think she cannot be comfy like that, but she must be xx
Ps. Image is from internet not mine.