They run a pretty tight ship, much like Singapore. Not much crime and very visitor friendly. The vendors can be aggressive, but you learn to deal with it. The Viets are now realizing just how much money tourist bring each year and want a bigger piece of the pie.
I would not worry at all about age groups. I am over 55 and never felt 'too old' or not fitting in. I think they are just glad you are there. Feb. to March is a good time to visit. Not so hot and not rainy season either. Send me a mesage if you want additional info.