Such a mind cannot be cultivated in a mere few months or years, but this does not mean it cannot be cultivated at all. If you continue your practice to cultivate bodhichitta, a time will come when you will be successful. For example, in the initial stage you may not even understand the meaning of the word bodhichitta. You might wonder how you could ever cultivate such a mind. But through repeated practice and familiarity, you will gradually come closer to such a mind.
It is the nature of conditioned things that they change depending on causes and conditions. So it is important to recall the advantages and benefits of such a mind and cultivate a strong determination to achieve it. Make ardent prayers. Whether you sleep, walk, or sit, you should think: "How good it would be if I could cultivate such a mind." Try to cultivate bodhichitta even on an aspirational level. If you spend your days in such repeated and persistent practice, you can definitely develop it. Make the determination to cultivate it even if it will take many aeons. As Shantideva prays in his Guide to the Bodhisattva's Way of Life:
As long as space endures
And as long as sentient beings remain,
May I too abide
To dispel the sufferings of all sentient beings.
--from Stages of Meditation by the Dalai Lama, root text by Kamalashila, translated by Geshe Lobsang Jordhen, Losang Choephel Ganchenpa, and Jeremy Russell
