If it's the Swift in Ware, MA, you can fish it anytime, although it's been tough lately with very high water. BUT, in that very clear water, those trout are notoriously difficult, and may prove frustrating if you're just starting out. Most folks are using 6-7x tippets and size 22-26 nymphs there.
Here's a suggestion. Get a copy of TU's book 'Trout Fishing in Massachusetts' and look for the DFW stocking reports on the web, and go visit some of the streams and ponds closer to where you live. You'll find those fish easier and much less picky.

If you do want to trout fish in MA this winter, drive up to the Deerfield river near Charlemont (instead of to the Swift) and fish some streamers. If you can get there when water is less than 1000 cfs, so much the better.