The “just under half” includes all ages (I clicked through to the poll from the article):

Respondents are very divided on Biden’s handling of the war, with just 49% saying they strongly or somewhat approve of the job he is doing in the area. 41% of respondents somewhat or strongly disapprove of Biden’s handling of the war, and 10% are undecided. This is starkly polarized by age: no respondents under 29 say that they strongly approve of Biden’s handling of the war, and 65% strongly disagree with it. Compare this to respondents 50-64 years old, who tend to side with Biden (59% are strongly or somewhat supportive of his actions) while just 7% strongly disapprove of his actions.

35% for just young people, just under half if you include everyone.