This is a site that contains all the details from the England & Wales census of 1901. The site is now working, BTW!
This is what you need:
The name of your relative (obviously!).
His age within + or - 5 years in 1901.
A rough idea of which part of the country he was born in.
You can now do a free search, and the site will tell you if it has the details you require.
But now, my friends you pay! You have to credit your account to the sum of £5, and then all extra details will be subtracted from this amount in 50 or 75 pence portions.
I have searched for all my grandparents who were around 3 or 4 years old in 1901 with 100% success. Also, once I have paid my fee, I have been given access to the original documents in which their details were painstakingly handwritten, as well as a modern easy to read version, all downloadable.
For example, I searched for my paternal Grandmothers listing. She was in the record as a 1 year old, but also noted were here many brothers and sisters. The address at which they lived was there, their parents, their ages, their occupations and even whether or not they were feebleminded or lunatic.
I even found that great great grandmother who was born in 1829 had moved in with my newly wed grandparents.
Give it a go!