Another antique! I think that dating the pen is fairly straightforward. On the barrel is stamped Mabie Todd & Co New York, but the section is stamped Swan 4500 M.T.B. This of course would refer to Mabie Todd & Bard which ceased in 1907, so I can reasonably presume that this pen dates from perhaps 1908 or thereabouts. Stamped also 4572 this represents a 4500 model with a short medium No 3 nib.
The pen incorporates a "plug feed" whereby the pen may be filled without unscrewing the section. There is also a gold overfeed, probably an early example. And the pen does what Mabie Todd claimed: it is always ready to write which it does very nicely!