OK....tried to use the spoiler and it didn't work.
Sorry folks....I know the answer, too, so if you don't want to read it, scroll quickly past the Asteriks*****
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If she's "about to be" 61, that means she's still 60. Obviously that's how come you can say she's "double" your age. You aren't speaking litterally, of course - You're just saying that 60 is double 30, so that's the "double" you're talking about.
If you recently turned 30, and she's just about to turn 61, that means when you turn 31, she'll be just about to turn 62. That will mean she WILL BE 62 at least for some period of time when you ARE 31. That will be the only other time she will ever be "double" your age. From then on out, you just creep closer and closer to being her age!
***OK, I didn't see that you actually added dates to this. Of course this answer all has to do with IF you had asked this about 4 days ago BEFORE she actually turned 61. (Now she IS 61.)
Before she turned 61, she was 60 and you were 30. Double (although not EXACTLY double.) Now she turned 61 and you're still 30. Not double. Soon you'll be 31 and she'll still be 61. Still not double.
But NEXT YEAR, AFTER October 6th, she will be 62 for about a month while YOU are still just 31. That number is once again double.
Again - It's not EXACTLY double. She will only be EXACTLY double ONE TIME in your entire lifetime. That has already past. (I'm too tired to figure out the exact date.)