Oh, I'm with you there...
Most of the good material on astrology is pre17th century. The truth is, the GD structure is based largely on the Agrippa material from Barrett's plagiarized
Magus, and they incorporated it withuout breaking it down as totally (at least in extant papers) as they did their take on Qabalah... largely because of the scholarship available at that point. The fact is the GD didn't DO much to astrology, probably because they didn't have the wherewithal or the sources. Much easier to muck around with QBLH post-Levi. There really isn't a good book on astrology in the GD system. Mostly new age sun sign slop. Kipp's book on Crowley is good, but not
about the basics. More of a rumination. A definite gap there, but onwe that will take a LOT of primary source scholarship, rather than Llewellyn-styl regurgitation.
So much material has emerged in the past 50 years.. which elucidates the underlying astro-bones of the GD. So, yes, older material is better.
As for friendly intros: Barclay, Frawley, Lehman, Zoller, Brady, Cornelius are all great... but they're all pretty demanding. Barclay is probably the friendliest. Frawley the funniest. I find that as I read I sort of absorb the topic osmotically.
Slow going, but worth it I think.