Not to spoil the party but scrambling in your senior years is certainly more commitment than when you're younger - any fall is likely to be more serious, and having a fall is more likely. That is simply the unfortunate reality, unfortunately shown by the 71-year old gentleman who died after a fall from Striding Edge 16 months ago during a 'perfect weather' day in July. There are many more who end up injuring themselves, or having a near miss.
However there are 69 year olds with incredible mountain fitness and I certainly plan to be bombing around the hills at that age (provided I get my cyborg knees installed by then). It certainly is less of a question of the route itself and more a question of you and your brother, how used to moving on mountain terrain are you, how confident are you and whether you want to keep it flexible on the day.
For example you could see how you feel on the day, if you feel uncertain - the Red Tarn-Catstye Cam route allows you some excellent views and it is handily giving you a nice circular.
Alternatively you might want to use the Grisedale valley route rather than back via Striding or Swirral and circle around via Dollywagon Pike - it's an excellent route on a good day and I usually find the Grisedale valley is a lot quieter than the main route up. Likewise with approaching via the west, or even White Side. There are plenty of options for the views where you don't need to be quite as committed/if weather isn't to your liking.
Just be cautious, if you aren't happy with conditions take an alternative route and make a good day of it regardless. Overall though I can think of little better than your plan, the idea of having a 'mountain picnic' with my brother from the other side of the world, both agaze at a sublime view after having completed a long-awaited route.