I get asked this question quite often. It is actually not that hard.
The lease agreement can be completed and signed by anyone that is older than 18.
You will need a witness and a black pen.
Each page must be initialed by the Lessee, the Lessor, the witness for the Lessee and the witness for the Lessor. That means four people are signing the agreement.
The two respective witnesses for the lessee and the lessor together with the lessee and the lessor must sign in full at the back.
I made a mistake. Now what? No problem. Neatly scratch out the mistake by drawing a single straight line through the mistake and amend by writing in the correct words, and initial next to the amendment. Both witnesses, the Lessor and the Lessee should initial next to the amendment.
Something is missing from the agreement. Now what? No problem. Neatly write in the missing words and initial next to the amendment. Both witnesses, the Lessor and the Lessee should initial next to the amendment.