Can a Bishop???

[[Dear Sister, if someone is professed as a diocesan hermit when they are in their mid to late twenties and their bishop changes down the line, can the new bishop ask the person to leave their vows and "come back when they are fifty"? Also, does canon Law say one has to be at least 30 to become a diocesan hermit? I heard this on a video called Joyful Hermit Speaks and it all sounded a bit off to me.]] 

The answer to both questions is no. Once someone is perpetually professed an incoming bishop will become the hermit's legitimate superior and will certainly have a voice in her life --- which will become truly meaningful only when he has gotten to know the hermit, understands her Rule, has met with her delegate(s), and perhaps had conversations with her pastor. However, he has no right or power to simply ask the person to leave her vows, nor would any canonical hermit or diocese allow this. In serious matters public vows may be dispensed, but this is a really serious situation requiring similarly serious grounds. It also requires attempts to resolve things otherwise and allows for appeals should the diocese move toward dispensation. 

The bottom line here is that under canon 603 one does not make vows to a specific bishop. One makes vows to God in a bishop's hands so that eremitical life may be a gift to the universal church but especially to the local diocesan church. Bishops may (and do) come and go, but one's vows do not. As I have written before, this is true whether an incoming bishop believes in c 603 vocations or not. To have canonical standing is to have certain protections in law; a new bishop (or an old one) cannot abrogate these rights on a whim.

The answer to the second question is also no. Canon Law requires one have completed their 18th year (or, that is, be 18 yo) in order to enter religious life but apart from this there is no additional or differing requirement re c 603. It is true that eremitical life is ordinarily seen as a second half of life vocation and I personally argue that younger persons (younger than 30 or so) consider entering a community where eremitical life can be lived; in this way they can be mentored and supported in the way a younger candidate for profession will need. Still, canon law says nothing about this specifically beyond the age for entering religious life. I'm afraid the videos you have mentioned are an unreliable resource regarding c 603, consecrated life, and even private vows.