I also love vintage, and the 60s and 70s were the heyday for these small-wheeled bicycles. Perhaps the success of the of early 60's British-made Moulton that triggered the teeny tiny bike craze. But whatever the reason, bicycle manufacturers of that era started cranking out these miniature marvels.
I have a couple of the mini velos in my collection and I do ride them. The Raleigh RSW and a Moulton "F" frame from 1964. I've made some modifications to the RSW such as adding a longer seat post and creating an extension for the stem. The Moulton, however, can actually be adjusted to work for me without modifications and it's pretty comfortable. But I worry that I'm too heavy, particularly for the rear fork, well known for failure.
Below is a random assortment of the offerings from that era. Several of the pics were borrowed from a blog entitled Mini Velo Vintage. The others are from the Embacher Collection. Both of these websites are worth a visit.