Not many old people who fear being shipped off to a nursing home fight back with a home arsenal and bomb threats. However, the inimitable Estelle Parsons has gleefully unleashed her inner anarchist with gusto to do just that in the dark comedy 'Velocity of Autumn,' which opened Monday night in a wry, spirited Broadway production at the Booth Theatre. Playwright Eric Coble presents the aging decay of the human mind and body as a necessary process replete with mordantly humorous and empathetic moments. He lightens the potentially depressing subject matter by providing plenty of comedic zingers to both Academy Award-winner Parsons -- here powerful and ingratiating -- and to her co-star, the equally skilled Stephen Spinella. Both of these pros imbue their characters with genuine poignancy, rueful humor and their own adept timing. Molly Smith's deft direction also creates a sense of urgency during the 90-minute showdown about a seeming no-win situation.