Youth Road Bikes

Hi there - my son Liam joined the club earlier in the year & has thoroughly enjoyed the Sunday & more recently, Monday evening sessions - simply terrific. He's turning 13 & growing! He has simply out-grown the 40 cm frame Trek bike he bought 18 months ago. He is now 5ft 7in (170cm) tall & still growing. Appreciate any advice on sourcing & purchasing a suitable bike would be appreciated.
John