Maximum ages for mortgage

Can anyone help?

I want to move house. need a mortgage. I'm 48 and main earner, misses is 59 and retires in 4 yrs.

What age up to I can have the length of mortgage over?
I did read that some base length on oldest earner and not youngest, is this correct?

Anybody had experience or know mortgage companies which give best max ages whilst taking younger partner age into consideration?

Thanks in advance