More life = more happiness?

I really do not want to make a statement or judgement. But something happened today & I realized that generalizing this could be ok...of course with exceptions, as usual.

Older people have seen more. They have lived more. So, they should be happier...right?
Well, I have mostly seen it to be au contraire.
Today, me & S were at the Garden. We have an organic plot, where we grow organic vegetables. Actually, we have just started.
So, I was respectfully sowing all my seeds. There is no way S would just sit & SEE me do it for 45 minutes. She had better things to do; Like digging the mud, getting all dirty, watering plants, blowing a dandelion. You know, STUFF.
And I let her do it. As if I have options, huh?
But I ask her to let me know where she goes(within the garden of course) & I check on her every couple of minutes. Knowingly, she would also raise her head every few minutes to meet my eyes.
On one such eye contact, I saw her lifting a big stone & putting it somewhere. I saw an elderly man, trying to tell her something. So, I went closer to check. He told me angrily, "Do you know what she just did?" Poor thing! By then she guessed something was wrong & she was the reason. She put her head down & made a :( face.
She had actually accomplished in lifting up a big stone but put it inside someone else's lot, as in where someone grew plants. The old man got so angry. I told him, "I am sorry. I will talk to her." I figured, it has already been done & the least I could do was talk to her & explain what she has done. He got so upset. He said, "The least you could do is supervise her" & went away. I smiled. At S. By then, she was expecting something from me. When I explained what she did upset that "thatha" she felt bad. And said she won't do it again. And then she followed me to our lot & never left my sight after that.
A very small incident. This old man would have been in his later 60's. I agree, at this age, plants mean so much. Still!
I was filled with, "Children are not born knowing everything...they don't understand what we want...heck! they don't understand what they want"...along those lines. But then I stopped myself saying I was trying to be a victim to this situation.
I decided then. I don't want to be resentful if I am old & alive. I want to enjoy & experience every moment of this joyous life. I realized that this moment...if gone, is gone. I don't want to save my life for when I am 60. I don't want to care for 60. I want to care for now. And my now is S. As long as I am a child WITH her, she will take care of that for me. What a blessing a child can be!