1. & 3. The state has enforced a minimum age limit to get married.
2. The Mumbai High Court has already passed a judgement regarding this.
4. If you consider Marriage to be a religious rite, and follow injunctions regarding it; and then you ought to treat consider religious injunctions regarding its dissolution. Else frame up a pre-nup agreement or get married in a court.
I don't know if muslims consider it unjust or not but because state has made it illegal. Personal laws cannot override what the state deems unfit.
The personal law boards have helped in ensuring that the state doesn't intervene in your marriage.
I didn't understand your point ?
The state took a more libertarian approach.
If you wish to follow your religious beliefs in regards to your personal matters such as marriage, divorce and succession then you should be able to do so, provided you follow certain conditions.
If you wish you can customize your divorce and succession using a pre-nuptial agreement and will respectively. This is again a choice given to the citizens.
You are confusing a few issues.
I want intelligentsia to be a part to make sure clerics wouldn't automatically be thrust as leaders, and orthodoxy wouldn't be allowed to reign.
I can't say for modern or rational, but if any practice is inhumane or unjust then the state intervenes. And if the intelligentsia ensures that the personal law boards organically evolve then nothing like it.
Removal of personal laws and imposition of UCC in India, would do more harm than good imo.