Section 17. If any tax, betterment or special assessment remains unpaid fourteen days after demand therefor, the collector, in the case of any tax, betterment or special assessment upon real estate, within two years from April first in the calendar year in which the assessment was made, and, in case of any other tax, within three years from said April first, shall collect the tax, together with all incidental charges and fees, in the manner provided by law.