Will trust as beneficiaries turn 25

A will trust for grandchildren has four remaining IIP beneficiaries, each of whom will become absolutely entitled to their share on reaching age 25.
The trust comprises a modest portfolio worth about £110k with chargeable gains currently £17k.
The eldest will be 25 in February and the trust only has another 4 years to run after this.
Is it reasonable to ask the eldest to bear the CGT, say £600, which will be incurred when investments are sold in order to pay his share?
The brokers do not consider it worthwhile, due to costs, appointing investments to him, with a holdover claim, and then selling on his behalf. He has asked for cash rather than keeping the investments himself in the longer term.