'SyntaxError: future feature annotations is not defined' during install

[jstmn]

Hi, when I get to pipenv install --dev --python 3.6.4 i'm getting the following error:

[~/chomper]: pipenv install --dev --python 3.6.4
Creating a virtualenv for this project...
Pipfile: /home/jstm/chomper/Pipfile
Using /home/jstm/.pyenv/versions/3.6.4/bin/python3.6 (3.6.4) to create virtualenv...
⠙ Creating virtual environment...RuntimeError: failed to query /home/jstm/.pyenv/versions/3.6.4/bin/python3.6 with code 1 err: '  File "/usr/local/lib/python3.8/dist-packages/virtualenv/discovery/py_info.py", line 7\n    from __future__ import annotations\n    ^\nSyntaxError: future feature annotations is not defined\n'

✘ Failed creating virtual environment
[pipenv.exceptions.VirtualenvCreationException]: 
Failed to create virtual environment.

it seems like the __feature__ package isn't available on python 3.6: https://peps.python.org/pep-0563/#enabling-the-future-behavior-in-python-3-7?

i'm on ubuntu 20