Bella Thorne Shows Off Her Now Legal Cleavage

Bella Thorne was bound to have a blast on her 18th birthday -- and so was her chest.

Bella showed up at Beso Restaurant in Hollywood ... sporting leather (mini-skirt) and a laced up top ... to celebrate adulthood with friends.

Her 23-year-old BF Gregg Sulkin was also there, because while it was Bella's big night ... it was even bigger for him. Just guessin'.