older than you think
Julian May sprang into view in the 80's with her outstanding tetralogy, The Saga of the Pliocene Exile. This is truly classic science fiction, and should be on everyone's reading list. She followed it up with a series of prequels, the Milieu trilogy, whose basic plot line she'd evolved before writing the Pliocene Exile books; she may even have written much of them beforehand as well. Be that as it may, the Milieu trilogy was a disappointment, though it had its good bits; and Intervention, the novel she wrote to bridge the two, is quite good.
More recently, she's written an odd, semi-farcical science fiction trilogy that I rather like but found hard to take seriously.
The Plicene Exile and Related Books