When a person lives with his/her partner, they both need to claim Universal Credit. The person should have joint control of the household, even when his/her partner is not eligible. The amount that will be received depends on the income and savings of the partner as the person.
If one of the partners has reached state pension age, both of you can still claim universal credit as a couple. But once both reach out the State Pension age, universal credit claims will be stopped.