In reply to Charliemitch:
Training time will depend on your current fitness level and how much time you can devote to training and being in the mountains. But even as a fit, occasional hill walker, you could be good to go later this summer. Also depends on how much you want to enjoy or endure the experience. More training = more enjoyment as you will be far better prepared for it.
I've taken quite a few people on the 24 peaks challenge, sometimes as part of big events, and many manage it just fine. Do it over 2 days and ideally get some support to shuttle your spare overnight kit, or pack light. There are numerous businesses here in the Lakes that offer shuttle services at very reasonable rates. Start nice and early both days, giving yourself max time to enjoy each day.
Other Lakes based challenges are:
Lakes 3000's: https://www.mountain-journeys.co.uk/lakes-district-challenge.html
Lakes 8 Peaks: https://www.mountain-journeys.co.uk/8peakschallenge.html
These are taken off our website, I'm not trying to sell you a trip (unless that's what you want), just shed some light on the options here in the Lakes.
If you want any more specific info about these challenges, I'm happy to help, e-mail via this site.
Mark