Robson's score included birdies on the first and 10th and an eagle three on the 11th.
Two shots back of him was Barclay Brown (Hallamshire), with Jack Maxey (Hornsea) on 74.
Brown had five birdies in his round, but also a double bogey and a triple.
Maxey had a more modest tally of two birdies, but fewer dropped shots.
Charlie Daughtrey (Rotherham) and George Heath (Woodsome Hall) carded 75, Max Berrisford (Skipton) and Ben Schmidt (Rotherham) 76 and Michael Hay (Middlesbrough) 79.
Sussex teenager Joe Sullivan, like Robson, got into what is the English Under-18 boys’ open championship from the reserve list and topped the leaderboard with a 66 in the first round.
It put him three shots clear of Gregorio De Leo, of Italy, and Eemil Alajarvi, of Finland overnight. Two players were tied on two under while a group of 13 that included Robson shared sixth place.
Defending champion Andrea Romano, of Italy, started well with a birdie on the first, but then was unable to make ground and closed with four-over 76.