ad ozne: (…) If I had been a chance to speak to your late grandmother, I would have asked “What is the best age to be ?” Have you ever thought about this in any depth? (…)
I know you asked JayB this question, but I’d like to try and answer it for myself as well.
As Jay already suggested it is not easy to find a simply answer. To me the best age would be the one where I feel most comfortable with the way my life goes. For example, I was not a very happy teenager (for various reasons). I would definitely not want to relive the years from 13 to 18. As a matter of fact, there are times when I still have to try and come to terms with some things that happened then. I guess we all have had similar experiences (to different extents).
However, I’m lucky enough to be able to say that when I was around 19 years of age things really seemed to change. I’ve had a wonderful life ever since (not that the years before that were like hell all the time but as I said I would not want to go back in time).
What I loved about being a child (not a teenager) was the care-free life I had. But this was not because the world was a better place to live than today (actually, I think in many ways it was not) but simply because I was able to live in my child-like world thanks to the love and care of my wonderful parents. It was their “cocoon” of love that allowed me to create my very own world of happiness.
I am also extremely thankful for the many years of friendship I share with a handful of people and I mean really “friendship” here and not just knowing someone and greeting each other when walking by each other in the street. I talk about deep relationships here. I have known my best friend for 26 years now. We live close by, we used to travel a lot when we were younger, I know her entire family (and vice versa) and we often share the joy and pain of life.
I love the age I’m at right now. And I love the fact that I can look back on many exciting and fulfilling years of my life while hoping to be able to add many more meaningful moments (I’m trying not to count in years).
I think it is what we all make of life that makes the moments we experience valuable.
I am learning this lesson the hard way right now again. Just about a couple of weeks ago my mother was diagnosed with an unfortunately very aggressive cancer at a progressive stage. The fear to lose her is immense, to watch her suffer causes me pain I can’t describe and yet there is this enormous feeling of love and gratitude between that invasive feeling of despair I try to fight. I don’t know how I would have dealt with all that as a kid. To be clear, there is NEVER a “good” time to lose a beloved one, no matter how old you are or how old the person is you fear to lose. Feelings like love escape that kind of measuring.
So, while we hope for the best and do whatever we can to help my mother, I think - as weird as this may sound - that knowing how many beautiful moments I have spent with her and how much love and warmth we feel right now amongst the pain and fear we are surrounded by, this is a good time for me to live. Any time that makes me feel close to the people I love and care about is a good time for me.
Apart from this maybe a bit philosophical approach, I’d say that I’m in the prime of my life now 
No more tedious teenage years, a great job, reasonably good health, a WONDERFUL family, fantastic friends and the financial independence and liberty to give back some of what I have been given also on a “material” level. Really, there isn’t much else I could ask for (except for hopefully many more years with my mom …).
Generally speaking, I try to focus on the present moment for it is the one that is all mine to explore and cherish. The past is gone (yet not without influence) and the future may not even be there for me to play any part in.
Carpe diem 