While ResultSet.next () returning only one result

There is return within your while . When return is found, the method ends immediately. Therefore, when you read the first result, the method ends without any other results being processed.

Assuming that you are managing the connections correctly with conn (I think this assumption is false, but that is a subject for another question), your code should look like this:

private static final String IDADES_SQL =
        "SELECT Idade FROM Pessoas WHERE Pessoas = ?";

private static String pegarTodasAsIdades(String pessoas) {
    try (PreparedStatement ps = conn.prepareStatement(IDADES_SQL)) {
        ps.setString(1, pessoas);
        try (ResultSet rs = ps.executeQuery()) {
            StringBuilder idades = new StringBuilder();
            while (rs.next()) {
                idades.append(rs.getString("Idade")).append("\t");
            }
            return idades.toString();
        }
    } catch (SQLException e) {
        e.printStackTrace();
        throw new RuntimException(e);
    }
}

Do not let PreparedStatement , ResultSet , and Connection be fields in your DAO, unless you know a lot, but very well what you're doing. And remember to always use try-with-resources .

There is a return in the middle of the while ... It is doing the while stop. Here's a solution:

private static String pegarTodasAsIdades(String pessoas) {
    query = "SELECT Idade FROM Pessoas WHERE Pessoas=?";
    try {
        ps = conn.prepareStatement(query);
        ps.setString(1, pessoas);
        rs = ps.executeQuery();
        String idades = "";
        while (rs.next()) {
            idades += rs.getString("Idade") + "\t";
        }
        return idades;
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return "";
}