Sheria house for business registration.

I guess it all depends on what area of specialization you want to target. Different areas require different registrations.
1. For construction contracts, of course you have to register with National Construction Authority as from this June. The old registrations by Public Works, Roads must be renewed by this new Authority.
2. For electrical works, you also have to register with ERC as a contractor.
Class C-2 KShs. 250/=, Class C-1 KShs. 500/=, Class B KShs. 750/=, Class A-1 KShs. 1000/= and Class A-2 KShs. 1000/=.
You or a director has to be qualified as electrician from university or polytechnic.
3. For public contracts, you must also be registered by KRA, get a PIN and a Tax Compliance certificate.
4. You also need a local authority license/Trade license
These are the basics, though depending on what particular contracts you target, there may be other requirements.
As for the decree that 30% of govt contracts go to youth, your guess is as good as mine. This is just that, a decree. Defining who a youth is in this country has been so political, remember we have a youthful president and deputy, youthful at 50? I am not sure how this decree can be enforced or even implemented. First, the youth have no capital and expertise to undertake govt projects.

@icecube, actually the 30% of govt contracts is actually being implemented right now and a lot of young people are having their business registered at the treasury so long as the majority partner is below 35 years. The business is then issued with a certificate which allows the company to compete for 30% govt contracts bila maneno.