Anna and Isobel are the most timeless, there's Annas and Isobels of every age.
I have to say, I do not agree with this!
Anna, sure, but I have never met another Isobel my age (40s), and I have lived and worked in the Antipodes, the UK and NY.
For the first time ever, I have a colleague called Isobel, but she’d be early 20s, so one of the first people to be given the name in its most ‘recent’ surge of popularity, beginning in the 90s.
IMO, it is definitely not timeless, it is very cyclical. No-one, but no-one was being given the name in the 60s, 70s, even 80s. It was considered very old-fashioned, and not in a good/‘vintage’ way!
To be honest, I’d say it’s ‘done’ for this cycle, so if you’re after something more genuinely timeless, I’d avoid.