i am going to visit the White House (literally) i have never even been to DC and i have no clue what to wear...please help!

i am heading to the mountains in colorado for the 4th and i have no clue what to wear? i assume pretty casual but i need some advice!

Going to the Amerian Idol concert tonight and not sure what to wear. i will probably be the oldest person there that is not escorting their children so i want to look young and hip but appropriate for my age????