Real estate baron Jay I. Kislak discovered a Fountain of Youth of sorts that springs from an inquisitive and acquisitive mind.

At 90, Kislak is wheeling and dealing in real estate, and he’s exploring history and art with the fervor of a man generations younger.

The patriarch of The Kislak Organization marked 74 years in real estate this year, 59 spent in Miami.

While he has long since appointed a protégé, Thomas Bartelmo, as president and CEO of the diverse family-owned real-estate businesses, Kislak remains chairman. And he is a regular at the headquarters in Miami Lakes.

That is, when he’s not off to Maine for the summer.

Or busy chairing a blue-ribbon commission named by the U.S. Interior Secretary to orchestrate the 450th anniversary in 2015 of the founding of St. Augustine.

Or jetting off to evaluate a possible acquisition. (Kislak recently looked at the potential for real estate development in North Dakota, booming with shale oil, but decided to pass.)

Kislak’s empire has gone through dramatic changes over the years. He built — and eventually sold — commercial banking, mortgage servicing and insurance firms.

Today, with annual revenue in excess of $28 million, his organization focuses on the commercial brokerage business started by his father, Julius Kislak, in Hoboken, N.J., more than a century ago; on owning a portfolio of apartments and other property (Kislak is on the prowl for more), and on managing funds of property-tax certificates, a niche created by the economic downturn.

Looking out his office window at a bustling interchange recently, Kislak mused: “I remember when they built the Palmetto Expressway and you could drive down it and never see another car.”

“The same thing with I-95: There was hardly any traffic,” said Kislak, a slender man with a signature mustache and a thick Hoboken accent that never faded.

Kislak moved to Miami in 1953 to grow the mortgage business, but his world view hardly dates to 1950s Florida. Already a book lover, he began pulling on a thread of Florida history, soon broadening his interest to the early Americas.

Over the decades, Kislak, bankrolled by a stream of brokerage commissions, mortgage fees and apartment rent, grew into a prominent collector of rare books and maps, manuscripts, artifacts and art to feed his fascination with the pre-Columbian era and the European exploration of America.

His wife Jean Kislak shares his passion for collecting. They met at a party for Andy Warhol; it would be her second marriage, his third. Their quest for art, history and collecting has taken them to all continents, even Antarctica.

“We don’t quit [collecting]. But we are going to quit,” said Jean, a former corporate art director. “Acquisition has always been a part of my life. I don’t know if it’s a sickness.”

In 2004, Kislak gave away much of the treasure. His foundation donated more than 3,000 rare maps, manuscripts, paintings and artifacts to the Library of Congress. The gift, estimated to be worth in excess of $150 million, is housed in the ornate Thomas Jefferson building in an exhibit that bears his name. Kislak also funds fellowships for studies of the collection, part of his diverse efforts over the years to support education. Among other things, his family foundation endowed the Kislak Real Estate Institute at Monmouth University, in West Long Branch, N.J., and has provided key support to a real estate program at Florida State University.