I am certainly no expert on this subject. At least from a practical standpoint, but I do know a bit about genetics (RNA/DNA) and a lot about cell growth, biochemistry and metabolism.
Certainly age matters from a plant perspective, some of the mothers out there are 5 even 8--->20+ years old.
My guess would be this, that a well matured mother is going to produce the best clone quality, and I agree sites matter, taking from new growth and internodes, or tips, is probably preferable as your cells are still young and flexible and differentiate into the required cell types (ie. roots, stems, leaf, ect.) also, my guess would be that hormone levels are higher in these types of tissues.
On the down side, I think that a plant that's overly immature isn't suitable for clones either, because DNA traits are generally going to be more fully expressed in a plant as it matures. It's going to have a "prime" age. Once the plant hits "elderly" stage, I don't know if it might get some sort of genetic frailty with reproduction or not, it's certainly an interesting subject, and I think that I would say away from chopping clones from a plant once it get's "REALLY" old, and try and make a backup plan or something, long before this becomes an issue.
Also, general plant health of the mother is going to have huge implications on the viability and vigor of the clones.
Here's a thread on this subject.
I just read this posted by Steep hill labs..not sure where they got it It's an old story... the Grower can't understand why the last three batches of clones from his mother plant 'Old Reliable' keep getting lower and lower potency values "....no matter how I change up the lighting...
www.thcfarmer.com
It's an old story... the Grower can't understand why the last three batches of clones from his mother plant 'Old Reliable' keep getting lower and lower potency values "....no matter how I change up the lighting, micro-nutrients, etc... originally my plants tested 15% CBDA & 6% THCA, now they down to 9% CBDA & 4% THCA."