Many players who are still eligible to play as juniors already enter enter senior tournaments. It is not uncommon to see, that some player plays qualifying at Grand Slam tournament and if they do not qualify, then they enter boys/girls competition.
It can happen that a player concentrates only on senior events, in which case they do not have points in the juniors ranking. But still such a player might want to enter at least some junior tournaments. For example, I think that junior grand slams are considered prestigious. If such player has enough points in senior ranking, but does not have point in junior rankings, can they enter the main draw? Or do they have to play qualifying?
I have noticed in Wikipedia article about tennis at the 2014 Summer Youth Olympics that one player entered based on being in Top 450 in the ATP ranking. However, Youth Olympic Games are kind of a special event, so it is possible that this was an exception and not a rule.
To summarize my question shortly:
Is it possible to enter junior grand slam tournament (or other junior tournament) based on ATP/WTA rankings (instead of junior rankings)?