He said such a decision has to be taken by the party and Gandhi himself.
"I have never said ''high time''... I have said he (Gandhi) has got full potential to become a good prime minister," Singh told reporters here.
"When he (Rahul Gandhi) becomes (the prime minister) depends on the people of the country, the Congress Party and himself," Singh said.
Gandhi, who turned 41 yesterday, is being projected by the party as the potential prime minister and future leader with senior leaders like Digvijay Singh noting that he has all the "qualities and capabilities" that are needed for a "good" prime minister.
Gandhi has set his eyes on Uttar Pradesh where Assembly polls are due in a year''s time to help his party capture power in a state where he led revival of the organisation by securing 22 of the 80 seats in Parliamentary elections in 2009.