I avoid the consultant title where possible, I'm currently contracting as an infrastructure architect which is about as high as it goes on the networking side. For that sort of level work (advising large companies - airlines, banks and the like, on network design, security, resiliency, future expansion) you need the big networking qualifications(CCIE or CCDE usually, though my Juniper qualifications are very in demand these days as they're rarer but a lot of people use the equipment).
You'll also want some background qualifications and experience to show you understand the application side (networks don't exist for their own sake). Experience is more important here but I have a current MCSE and RHCE which are both useful.
Then you'll need at the very minimum 5 years experience in fairly decent roles, preferably some experience in either finance (best) or service provider environments. When I say 5 years, I mean however much time on helpdesk, 1st/2nd line support, then 5 years of network engineer roles or similar.
Lastly you need to be pretty talented, if you can't easily understand the technologies early on then you'll find it difficult to design complex solutions based on them. Basically you need to have found the CCNA an absolute doddle when you did it.
Upside is you can demand upwards of £450 a day contracting, which means you can choose to work 9 months a year if you wish, which isn't a bad lifestyle.
I've made it to this level by my mid twenties, so it's very achievable (though you'll obviously end up disillusioned, cynical...and rich of course). I gave up on Stroud at 18 though...so you've got some catching up to do...
More practically, consulting type roles often want an CCNP / MCSE and that'll do nicely for advising a little 200 user company on what they need to do. It maybe gets you a little tied to the professional consultant thing though, I'd prefer advice from someone who's done it themselves for years, not been telling other people how to do it for years.
