We started DS in one at 4 months, he used it for 2 weeks and never again, he hated it lol.
When they can support their head well..
If he slumps over, take him out.
they are good form "6 weeks and up" but as soon as they can support their head well it's ok.
My oldest was probab;y 7-8 weeks and only used it a few times cuz his legs where too chunky lol my second son was also about 6-8 weeks old and loved it until 4ish months when he could sit on his own.. They both had amazing head control though.
Two months is fine as long as hes not slumped over when sitting in it. We did at 2 months but DS hated the bumbo seats. So we switched to one of those little booster seats with the tray in front. He loves it.