Don't find her very attractive.
People keep raving on about how sexy she is for an older woman (and at 65 she is pretty old) but frankly I think her looks are pretty overrated. She was pretty enough when she was a young woman in her 20s, but that was a hell of a long time ago. Apart from maybe that Michael Parkinson interview, I don't think I've ever found her particularly sexy onscreen, the earliest thing I've seen her is Long Good Friday (when she was about 35, which isn't really old). By the 1990s she'd become lined and haggard (which probably helped with her role as a ball-busting Detective Chief Inspector in Prime Suspect) and as she gets older, her least attractive feature, that really long pointy nose, just becomes more and more witchy.
Obviously she's a good actress and not some Hollywood bimbo and I suppose if she's a sex symbol she's sort a "thinking man's sex symbol" or maybe a older man's sex symbol but I do find all the fawning over her supposedly sexiness a bit silly. All right she has a pretty good body for her age in those paparazzi bikini pictures but I just can't be that attracted to a woman who's 10 years older than my middle-aged mother.
She definetely wasn't an actress who managed to resist aging like Kim Cattrall or Michelle Pfeiffer or other examples I can't think of right now (I'm sure there's plenty). Even Joanna Lumley has sex appeal now than Mirren (although it does feel a bit wrong thinking of a woman so much older than me (I'm 26) in that way).