"21 we are going to be doing," Trump was quoted as saying in a release that pooled press comments he made at a meeting with vaping industry executives, public health advocates, lawmakers and administration officials on Friday.
The number of vaping-related deaths in the United States grew by five over the past week to 47, and nearly 2,300 cases of lung injuries have been reported, the Centers for Disease Control and Prevention (CDC) said on Thursday.
Some lawmakers criticized Trump earlier this week for his apparent walk-back on a planned ban on flavored e-cigarettes, which has been identified as a new addiction and particularly among young people.
Trump defended his decision to propose an age limit on vaping products rather than an outright ban by comparing the effects of illegal liquor consumption during the 1920-1933 prohibition on alcohol in the United States.
"You watch prohibition... if you don't give it to them, it is going to come here illegally," Trump said referring to e-cigarettes. "They could be selling something on a street corner that could be horrible... they are going to have a flavor that is poison."
The minimum age to purchase any tobacco or vaping product is 18 under US federal law. But more than one-third of US states have already raised the sale age to 21. A federal law raising the purchase age would require congressional action.