I wouldn't say Danny DeVito reached the height of his career in his 60s, maybe from your perspective if you're younger. He had a resurgence in popularity with Always Sunny but he rose to prominence when he was on Taxi.

I'm only in my mid 30s but I already knew Danny DeVito from Twins and Matilda among other things. I'd argue the reason why Always Sunny was able to grow in popularity was after they added him to the show. Since he was already an established actor and director who brought even more fans to Always Sunny as it started to rise in popularity.