...I must say that my personal experiences correlate with those described by Baldur, Snowi. No doubt there are many lesbians with more or less tolerant views on intergenerational attraction, but I have not noticed them being any more open-minded about the subject than any other group of teleiophiles, even if they themselves had been subject to bigotry and difficulties with family and friends as they grew up and became aware of their preferences.
I had two lesbian friends (a couple) whom I considered to be very good friends turn on me last year after they pretended to be supportive and tolerant of my preferences for AGs. Though I am fully law-abiding, I do often date younger women in the age group of 18-early 20s (my current love interest, whom I recently met, is one month shy of her 19th birthday). These friends of mine, Nancy and Jenny, had a rough time gaining acceptance from their families when their predilections became known, particularly Jenny, who was kicked out of the house in a very dramatic fashion at age 20 when it was discovered she was dating Nancy. I was nothing but supportive of the two of them (Nancy is now 30), and I thought they reciprocated, as one would think they know better after what they went through themselves. I was, sadly, to be proven wrong.
It turned out that they were only pretending to be accepting of my preferences. This was revealed one day a year ago when I was arguing with Nancy over the phone over money that she owed me and welshed on her promise to pay me back a week later when I desperately needed it, and when the argument became heated, Jenny suddenly began texting me highly sarcastic and outright cruel attacks on my sexuality. After all they themselves went through, all I did for them in regards to both support and financial assistance when they needed it, and considering how close I thought Nancy and I was? I was extremely hurt by this, and I have refused the periodic attempts that Nancy has made to apologize to me since then.
And that's not all. A year before that, when Nancy was courting a 27-year-old lesbian named Merrin who lived a few hours drive out of town, she took me with her to meet and hang out with Merrin. We seemed to have a good time, and Merrin was very cool with me to my face, but the following day she made a series of disparaging comments about me to Nancy, including calling me a "pedafile." And do you know why? Because when we were hanging around at the mall, I noted in passing that I found a 21-year-old woman attractive. Can you believe that? And Merrin had likewise experienced difficulties with getting her family to accept her lesbianism as she matured, according to Nancy.
Hence, my experiences do not suggest that lesbians, as a whole, are any more open-minded about this subject than any other teleiophile. However, as Baldur mentioned, they may be more tolerant of intergenerational relationships if the older partner is female rather than male. So my advice is, please be cautious around your gf's friends, and be careful which ones you trust.