Should LPs ask for a shorter term for a venture capital fund than 10 years, it may be an indication that the LPs do not understand the asset class and are not aligned with the fund and its managers. Proceed with caution - further discussions may be warranted.
Imho, optimal term depends more on sectors focus than stage focus. But usually 10 + 1/2 extension option are the standard terms. But some sectors required more than 10 years to bring intresting returns.