I don't think their age is the most important factor. Look at how cool the Beatles currently are in the 16-19 bracket.
True, just bought my 15 year old, at her request, a Beatles journal, tshirt, notebook...I had to explain the iconic Abbey Road cover and then pointed out U2's photos there w/ Green Day. THAT should hold some sway!
Beatles' coolness comes from the past, when they were young and creating their legend. Thus, they likely would now receive the same ageism issue U2 has. (ageism? sp?)
And, seeing how dd now realizes how terrific the Beatles are, hopefully it won't be long for her to come to her senses about U2. She does love the line 'Every beauty has to go out w/ an idiot.' She was telling me about a couple she can't quite see together and I shared that line. She posted the entire verse on her Facebook, even giving U2 the credit! Score 1 for U2!