To change the coinbase maturity, in the qt subfolder, the transactionrecord.cpp file should be changed to set the required number of blocks that are to be found before the mined coins can be spent:

  if (nNet > 0 || wtx.IsCoinBase())
    {
        //
        // Credit
        //
        for(unsigned int i = 0; i < wtx.tx->vout.size(); i++)
        {
            const CTxOut& txout = wtx.tx->vout[i];
            isminetype mine = wallet->IsMine(txout);
            if(mine)
            {
                TransactionRecord sub(hash, nTime);
                CTxDestination address;
                sub.idx = i; // vout index
                sub.credit = txout.nValue;
                sub.involvesWatchAddress = mine & ISMINE_WATCH_ONLY;
                if (ExtractDestination(txout.scriptPubKey, address) && IsMine(*wallet, address))
                {
                    // Received by Bitcoin Address
                    sub.type = TransactionRecord::RecvWithAddress;
                    sub.address = EncodeDestination(address);
                }
                else
                {
                    // Received by IP connection (deprecated features), or a multisignature or other non-simple transaction
                    sub.type = TransactionRecord::RecvFromOther;
                    sub.address = mapValue["from"];
                }
                if (wtx.IsCoinBase())
                {
                    // Generated
                    sub.type = TransactionRecord::Generated;
                }

                parts.append(sub);
            }
        }
    }
    else
    {
        bool involvesWatchAddress = false;
        isminetype fAllFromMe = ISMINE_SPENDABLE;
        for (const CTxIn& txin : wtx.tx->vin)
        {
            isminetype mine = wallet->IsMine(txin);
            if(mine & ISMINE_WATCH_ONLY) involvesWatchAddress = true;
            if(fAllFromMe > mine) fAllFromMe = mine;
        }

        isminetype fAllToMe = ISMINE_SPENDABLE;
        for (const CTxOut& txout : wtx.tx->vout)
        {
            isminetype mine = wallet->IsMine(txout);
            if(mine & ISMINE_WATCH_ONLY) involvesWatchAddress = true;
            if(fAllToMe > mine) fAllToMe = mine;
        }

        if (fAllFromMe && fAllToMe)
        {
            // Payment to self
            CAmount nChange = wtx.GetChange();

            parts.append(TransactionRecord(hash, nTime, TransactionRecord::SendToSelf, "",
                            -(nDebit - nChange), nCredit - nChange));
            parts.last().involvesWatchAddress = involvesWatchAddress; // maybe pass to TransactionRecord as constructor argument
        }

We have to change the transaction confirm count in the transactionrecord.cpp file to set this parameter, as per our requirements.