Yep, the idea was always to have Senators be slightly older than Representatives. Alexander Hamilton explained in Federalist no. 62:

>The qualifications proposed for senators, as distinguished from those of representatives, consist in a more advanced age [...] A senator must be thirty years of age at least; as a representative must be twenty-five. [...] The propriety of these distinctions is explained by the nature of the senatorial trust, which, requiring greater extent of information and stability of character, requires at the same time that the senator should have reached a period of life most likely to supply these advantages [...]

Although I'm not sure if Hamilton had quite these ages in mind. I did some quick Wiki-searching and put the dates of birth of all the first Senators in LibreOffice, and found out that the median age of the 1789 Senate was only 47.47 years.

I cannot find a clear value for median age in 1789, but based on what little I've found, the median age certainly wasn't 20 so the age difference between Senators and the general population was a lot lower at the first Senate meeting.