Hi Delper,
1. From the limited amount I've heard Cognosis have blue chip clients within FMCG but none in retail. They work with alcohol and tobacco so not a company if you have an aversion to either of these areas. Seem to be growing strongly (advert on TC) and compete with McK for most of their work.
2. I work with one from MBB and they are incredibly particular; you'd expect nothing less. The standard of application they receive are very high (1st from Oxbridge, blue chip or consulting internships and extra-curriculars are standard for graduate entrants). I'd agree with Zakmba that age doesn't matter so much as what you've done with your time. They need very fast progression, ambition, responsibility and a superb analytical ability.
Not knowing very much at all about your background it's hard to say and this may sound harsh but you need more than a 2:1 and a retail grad scheme - something different that shows you're top tier worthy. No harm in applying but you've got to have your game face on!
Good luck!