Roger, assuming he is not married to a British Citizen, the tests include :-
- not out of the UK more than 450 days in the five years up to the time when IND receive the application, and also
- not out of the UK more than 90 days in the one year up to the time when IND receive the application
Now "3 months" is about 90 days so I think your brother needs to be careful here. He also needs to take into account any other absences from the UK since April 2005, in order to work out the number of days out in the last year.
There is a bit of leeway on those 450 and 90 day numbers, but not a lot.
So to summarise, he could be causing problems for himself and might need to delay his application.