Robert Irwin is feeling the love! The famous animal conservationist celebrated his 18th birthday on Wednesday, in Australia, and received and outpouring of sweet messages from his friends and family.Robert's older sister, Bindi Irwin, celebrated the big day with a heartfelt snapshot of herself and the b-day boy taken back during her wedding, while standing in front of a giraffe named Forest.«Forest’s face behind us says it all… happy 18th to the very best.