Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Vaccine | Minimum Age at 1st Dose | Number of Doses | Dose | Minimum Interval Between Doses | Route |
| --- | --- | --- | --- | --- | --- |
| Bacillus Calmette-Guérin | Birth or anytime after birth | 1 dose | 0.05 mL | none | Intradermal |
| Diphtheria-Pertussis-Tetanus Vaccine | 6 weeks old | 3 doses | 0.5 mL | 6 weeks(DPT 1), 10 weeks (DPT 2), 14 weeks (DPT 3) | Intramuscular |
| Oral Polio Vaccine | 6 weeks old | 3 doses | 2-3 drops | 4 weeks | Oral |
| Hepatitis B Vaccine | At birth | 3 doses | 0.5 mL | 4 weeks interval | Intramuscular |
| Measles Vaccine (not MMR) | 9 months old | 1 dose | 0.5 mL | none | Subcutaneous |
Question:
Name the least age for the 1st dose for 3 doses of 2-3 drops
Answer:
6 weeks old