When is the best and happiest age period in life?

Easily childhood innocence.

happiness is not measured by years

When you are 5 you want to be 10
when you are 10 you want to be 16
when you are 16 you want to be 18
when you are 18 you want to be 21
when you are 21 you want to be 30
when you are 30 you want to be 21
.....

0-10!

if u have complete 100 % awareness their is no specific best and happiest age in life . complete life time is blissful.

Each age period is generally characterised by major flaws and major greatness.

When you're below ten, you are perpetually eager, happy very often, sometimes carefree, and rather innocent, but you don't recognise any of that because you're so new to the world, and you spend all your time waiting to grow up.

With 11-20, which is known to be the most stressful period of a human's life, there is a lot of fun and happiness and more innocence than at later years, but there's also the aforementioned stress and the waiting to grow up so everyone will "stop treating you like a kid" and so you can drive, drink, party, live alone, et cetera.

With 21-30, you're starting off your real adulthood, and, while having fun, you have to start being mature and have to start taking hold of your life, i.e. getting a job and home, which can be very difficult and stressful things.

I'm going to say 10-21!
10-yay! double digits!
13-yay! i'm a teenager now!
15-yay! i'm learning how to drive!
16-yay! i can drive!
18-yay! i can buy cigarettes and move out!
21-yay! i can buy alcohol and get sloshed!

not a whole lot happens after that.

21-30
I just turned 21 and it looks like its gonna be a whole lot of fun. Can't wait!!

The part yet to come...I'm 15, so I look forwward to 21-30 right now....

well depends on your demographics

Western world: 0-10
everywhere else:21-30


but its really when you discover your self truly when you are happiest

I'm going to say 21-30.....for me anyways