Residential rental income exceeds 20 lakhs- gst registration required?

No, Since you are engaged in supply of service which is wholly exempt from tax

The fact that your turnover/rental income is exceeding 20 lakhs is not relevant

Since you are exclusively engaged in an exempt supply

i.e renting of residential dwelling for residential purpose

Refer -> Section 23(1)(a) of CGST act 

Thanks

No you are not required to get registered under GST.

Rental Income received from letting out Residential Properties for residential use is EXEMPTED from GST by virtue of Notification No. 12/2017 - CT ( Rate ), dated 28.06.2017.

So you are dealing in exclusive supply of exempted services. Hence you are kit required to take registration under GST by virtue of Provision of Section 23 of the CGST Act 2017.

Warm Regards.