Is there a link between hair loss and prostate enlargement?

Yes. Male pattern baldness and BPH (big prostate) are both associated with increased level of male hormones (androgens such as testosterone).
Yes. Yes, studies show an association between BPH and male pattern baldness. While there is a link to male androgens, it is interetsing to note that testosterone levels decrease with age while the incdence of BPH increases with age. The common link may be an increase in the levels of dihydrotestosterone as testosterone levels decrease - this explains why some meds for BPH are also used for baldness.