Your young player's rating is not very good but he showed decent ability to score (unless the opponents are very weak). As he is young and trains decently, I usually give him some time. Some young players may improve performance after 1 or 2 seasons. It is probably because they will find a right role in the team and simply develop necessary skills. As long as he can improve in quality (and so does market value, for low levels), the time keeping him is not wasted.
Strikers generally have better statistics. But this is relative speaking. I also consider overall team ratings and performance as well as statistics of whole league. As I remember, my best strikers in the past might have average ratings above 8. In last 3 seasons, my teams could not dominate in league as before. Total scores in league matches also dropped. My strikers' average ratings dropped to low to mid 7. But I still consider some of them well playing.
My L23 team have 42 points after 22 matches and tied at top the league table now. The team does not dominate but plays well and won some close matches. There is only 1 regular starting ST who scored 17 goals in 24 matches. This is about one forth of my team goals in this season. His average rating is only 7.5. But he can score many goals in matches even if his rating is 7 only. He is only a low 5 star striker. Only ranked 2nd or even 3rd among my strikers in qualities. But he is reliable enough that I usually only start him as the only striker. I trust that he can carry my team to win some matches without great match rating.