No, most refer to it as Retirement VISA.
But whatever, in UK you cannot have pension if under 55., or (pathetic) State jobbie under 67.
In all my 10 Retirement Extensions, I have never been asked where my monthly transfer comes from....house rental, Pension fund, or sister's immoral earnings. They don't give a monkey's.
What you send in gets taxed, the rest, in your own country, is yours. (Unless you tell them )