If a 20 year old in Yeshiva E”Y wants to go to Meron on Lag B’Omer, can parents tell him no?
“My own limited baal habatish take on it”
Even if going to Kever Tzadikim is a Miztva and an apsect of Avodas Hashem; clearly there is no obligation to be doing so. Once there is no obligation then for sure KAv”A carries the day?
The issue regarding the child’s obligation to listen to his parents regarding this, is the subject of controversy. Since your gong is not really servicing your parents, it perhaps is not included in Kibud av v’em. On the other hand, not listening when you parent told you no may be included in לא יסתור את דבריו, not to contradict what the parents tell you. The poskim say, that due to this controversy, if listening to the parent will cause undue hardship to the child then he does not have to listen, but otherwise he should.
In the final analysis, it is hard to say that it is an undue hardship not to go to Meron, but it really depends on the individual circumstances, because in certain circles, not going is very difficult.