My official C64 entry came to 26 bytes. But subsequent to the deadline I came up with this 25-byte version:

CRLF = $AAD7
PNT = $d1
*=$80d

start
bcc right
dey
bne skip
jsr CRLF
right
iny
cpy #19
skip
inx
xaa #$0f
bne start
lax #'*'
sta (PNT),y
inc $65
bpl start
rts
end