Short version -
Moved my seat forward 3/8 of an inch, bike handles better, everything so much better it is hard to believe.
Am 65, bought new bike. First ride 8 days ago.
LBS looked me over, said this is your size, and that was it.
Bike felt twitchy, squirrely - I haven't ridden in 50 years. Finally got the seat high enough, learned that steering is mainly thru your hips, put outside pedal down with weight down on turn, etc. all that helped. began to feel like I am more confident of control.
Searched forum on "twitchy steering" saw a thread where poster stated moving seat forward a bit changed center of gravity and helped a lot.
I thought, I need to give that a try - then forgot to take wrench with, went out with my wife - feeling better and more confident.
Brought my wife home, made sure I had the correct tools, went back to paved bike path and moved seat forward 3/8 of an inch.
Alll of a sudden, damn! this is what it is supposed to be like!
Had a stunning 20 mile ride.
Pedaling was a lot better, felt like my feet were in clips, bike handling beautifully.
Kinda like I would just think where I want to go and the bike goes. All the stuff I had been fighting - just went away.
Don't let anybody kid you - fit is everything!