Donald Trump forgot his youngest son’s age this week shortly after he mocked President Joe Biden’s own mental acuity, RadarOnline.com can report. Trump forgot his son Barron’s age on Thursday during an interview with Univision 51. The embattled ex-president’s blunder came as he and Univision 51 reporter Marilys Llanos discussed Barron’s upcoming political debut at the Republican National Convention in Milwaukee, Wisconsin in July. Barron, who turned 18 on March 20, was recently named a Florida delegate for this year’s RNC. “Well, to me that’s very cute because it’s a very young guy and he’s gr…