Christina Aguilera celebrated her 40th birthday in sassy style on Friday, and then took a moment to share a reflective and insightful birthday message with her fans.The Drrty singer took to her Instagram that evening to pen a note written to her new age, packed with uplifting, empowering and inspirational thoughts as she embarks on this new decade.'Dear 40,' Xtina began, 'What a beautiful concept… To not only be "turning" 40, but to be ARRIVING at 40!' View this post on Instagram A post shared by Christina Aguilera (@xtina) Aguilera went on to say that she always has 'embraced' getting older.'I am forever an old soul and I appreciate the wisdom, grace and beauty that comes with each new year of life.' She also touched upon the unprecedented.