Minor's property can not be sold without permission of court.  

This sale is illegal. No title to the property is transferred to you. 

This can be treated as a fraudulent sale. 

You have following two option. 

File criminal case against the seller. 

File money recovery suit in civil court. 

You can not get the title to the property because sale is totally illegal.

If property was in name of minor then court permission ought to have been obtained by mother before sale  of property

2) minor should have within period of 3 years of attaining majority filed suit to set aside sale

3) if no such suit is filed claim would be barred by limitation 

The law is very clear. If the property belongs to minor then you need courts permission. The minor can take action

1. Yes .... it is true that Minor's property CANNOT be sold, by parents /anybody, without proper order of the local Civil Court.

2. However, in the case instant, the claim is now time barred for the minor (now major boy) to file any claims on you or to get the sale deed rescinded /revoked.  However the Boy can file claim against his parents, for recovery of the consideration amount received due to sale of his property, BUT definitely not against you.

3. If you apprehend some legal proceedings and you do not wish to fall into litigation's etc.... You can amicably settle with the major boy, by executing a Settlement Deed and taking an Indemnity Bond from the Boy. (This does not seem necessary, since the Court would not grant any relief to the now major Boy).

1. Court's permission is mandatory for selling any property in the name of a minor,

2. if the permission is obtained by the parents No risk to you,

3. if the permission is not obtained, your title to the property is illegal,

4. the boy can file a case against his parents not against you and can claim the property consideration,

5. he had to file the case within 3 years after attaining majority,

See as such before filing suit in this case prediction cannot be made is as your title is good , suit is barred by limitation also if you think they can file suit file a caveat before the court so that in case there is any suit you may be intimated before passing any order by the court.

First he couldn't file case on limitations ground as per limitations act. 

Secondly if he still succeed in filling the case than you have rights on adverse possession clause.

Any such property sold by the Guardian must have the reason for sale in sale deed and that will be the merit for contest in case any such litigation comes but will not effect your rights on the possession as you have purchased property in 1978 and this is more than 30 years.

The minor can claim the property within three years after becoming major by age.

No claim for the property had minor's interest and was sold during the minority of the child shall be entertained beyond three years after the minor becoming major by age, it is not maintainable in law.

Hence you need not be worried on that aspect at this stage.

1. The suit by boy will not maintenable after such a long time as he have turned major 12 years ago and he must have filed the case at time when he became major. 

2. You can take defence that he had knowledge about the sale at time when he turned 18.

The minors property cannot be sold without the permission from court. Even if sold it, the minor has the right to challenge it on his attaining majority. PETITION FOR PERMISSION TO SELL MINOR'S PROPERTY UNDER THE GUARDIANS AND WARDS ACT .

Minor could have challenge the sale within 3 years on becoming major - up to 21 years of age. Your title is absolutely  secure.

He can challenge the sale on the grounds that he was a minor and hence the property was sold against his interest.

But he attained majority 30 years ago. Now he cannot challenge this.