I just made a starter this past Saturday from a vial of harvested pilsner yeast strain I had back from Feb of this year... Basically 8 months old.
I did a 1.5L starter in 1.04 wort... Pitched the yeast vial on Saturday (mid-day). Showed no activity all of Sunday. Monday morning, finally had some life. By Monday night, looked to be finishing out. Cold crashed Tuesday morning and created a new starter (3.5L) last night, pitching the decanted yeast into the new starter. Looked to be quite good growth of yeast compared to what I put in from the first starter.
This morning, I had yeast all over the table from the krausen blowing off overnight. Must have taken off in hours, and vigorously. Nice healthy yeast ready for the lager this Saturday.
FWIW, yeast estimator tools said I had anywhere from 0-20% vitality remaining in my vial. It took nearly two days to even get going, but it all seems all good to go in the end.
If you already pitched it, if anything, the yeast will be stressed if the pitch rate was too low. You may end up with some differing flavors than expected.