WASHINGTON — In a homecoming tinged with nostalgia and an unspoken sense of farewell, President Obama on Monday welcomed his oldest living predecessor, George Bush, to the White House, where the two men, separated by nearly four decades but united in their fervor for volunteer service, presented an award to a retired Iowa couple.

Appearing together in the East Room, Mr. Obama and Mr. Bush, who is 89, bestowed the 5,000th “Daily Point of Light” award — named after Mr. Bush’s signature initiative on volunteer service — to Floyd Hammer and Kathy Hamilton, who founded a nonprofit organization that delivers free meals to hungry children in 15 countries.

Paying tribute to Mr. Bush for “how bright a light you shine,” Mr. Obama recounted how his predecessor began awarding these prizes while still in the White House, and has continued to hand them out every day since he left the presidency in 1993.

“When you do a parachute jump at the age of 85,” Mr. Obama said, gesturing to a smiling Mr. Bush, in a wheelchair, “this is somebody who is not going to slow down anytime soon.”