Hi Henrik
There isn't a universal rule and there are lenders with no maximum age limit for the mortgage, so in that respect the decision really boils down to how affordable the mortgage will be in the later years - that may be of no consequence if you have a plan for having no mortgage by a set time.
So, the rules:
There are some, but not too many, lenders that would stop being available if you went past age 65.
The next landmark age is 70
Most of the lenders that go past age 70 won't have maximums, although 79 and 85 sometimes crop up.
I'm a mortgage broker - the software I use enables me to put age into the equation so that I can produce league tables that only include the lenders that can deal with the age required. By all means give me a call.
Adrian Garside