Hypothetically speaking, I am a 50 something year old adult, but I tell people I am 40 or 30 something. Why? Well... “I don't feel like a 50 something, I still enjoy embracing life to the fullest and having the time of my life! I don't want others to treat me differently because I am older, so I'll just tell them the age I feel. What's so wrong with that?” Aside from how people will treat you differently when they find out you lied to them, you are not being true to yourself. You might say, “but I'm being true to how I feel,” to that I must disagree.