Ospreys wing Tom Prydie has been named in the Wales Under-20 squad two seasons after making his senior debut.
Ten players including, Ospreys fly-half Matthew Morgan, have been omitted because they are likely to be on regular regional duties.
"The 10 players excluded will be available for the Junior World Cup," said Wales U20 manager Mark Taylor.
"Therefore it is important those who are selected for the Six Nations take their opportunity to push their case,"
Wales new U20 coach Danny Wilson has named an initial 36-man training squad which will be reduced to 30.
With 10 players missing - including Tom Habberfield, Harry Robinson and Rhys Patchell who are on international Sevens duty - a number of players have been drafted in giving them an unexpected opportunity to stake their own claim.
There is an extra incentive of doing well with places up for grabs for the World Cup squad which will take part in June's Junior World Cup to be staged in South Africa.
Wales begin their Six Nations campaign against Ireland at Dubarry Park on Friday, 3 February.
Wales Under 20s Extended Training Squad
Props: Rob Evans (Scarlets, Tom Davies (Blues), Samson Lee (Scarlets), Dan Suter (Ospreys), WillGriff John (Blues). Hookers: Kirby Myhill (Scarlets), Jack Dando (Blues ), Darran Harris (Blues), Jac Hopkins (Cardiff), Jamie Sollis (Dragons). Second Rows: Matthew Screech (Blues), Jack Jones (Ospreys), Rhodri Hughes (Ospreys), Jonathan Gardiner (Leicester). Back-rows: Ellis Jenkins (Blues), Daniel Thomas (Scarlets), Dan Crimmins (Cardiff), Ieuan Jones (Dragons), Rueben Tucker (Blues), Dan Baker (Ospreys). Scrum-halves: Jonathan Evans (Dragons), Joshua Davies (Dragons), Jack Moates (London Irish). Outside-halves: Jordan Williams (Scarlets), Sam Davies (Ospreys), Lewis Williams (Blues). Centres: Rheon James (Scarlets), Thomas Pascoe (Blues), Cory Allen (Blues), Nathan Edwards (Bridgend), Luke Williams (Dragons). Wings/full-backs: Luke Morgan (Ospreys), Iolo Evans (Scarlets), Jake Randall (Scarlets), Tom Prydie (Ospreys), Ross Jones (Ospreys).
Not considered/unavailable for selection:
Second row: Cory Hill (Blues). Back-rows: Thomas Young (Blues), Luke Hamilton (Blues). Scrum-halves: Rhodri Williams (Scarlets), Lewis Jones (Blues), Tom Habberfield (Ospreys). Outside-halves: Matthew Morgan (Ospreys), Rhys Patchell (Blues). Wings: Eli Walker (Ospreys), Harry Robinson (Blues).