From what I remember, it was Finn's choice to do another year at U23 level. Wanted to show off the rainbow jersey and win a bit, and I think there isn't much harm in keeping a lighter training/racing load at 19 (in terms of long term success or motivation). Keep it low-key and low pressure.
Hopefully he will do another pro stage race or two given this started so well and got cut short. Something like Burgos, l'Avenir, then an Italian autumn and WC/EC.