A pensioner is a person who collects a pension, most commonly because of retirement from the workforce. This is a term typically used in the United Kingdom (along with OAP), Ireland and Australia where someone of pensionable age may also be referred to as an 'old age pensioner'. In the United States, the term retiree is more common, and in New Zealand, the term superannuitant is commonly used.
If the amount is been invested in lawful business away from unlawful business e.g. alcohol, pork, usury etc, then the income from it will be lawful. Such income can not be fixed by a percentage from the capital, but it must depend on the profit if any.
Fixed amounts given by non Muslims is allowed for the Muslim to receive and utilize in lawful needs and aims.
Yes it is allowed for every Muslim to invest his money after being sure that money will not be invested in unlawful business i.e. alcohol, interest, etc.
Khums will be applicable on the investment on the date of Khums.