All 4 of our dogs have been rescues and older. The oldest was 14 when we adopted her, she was with us for 1 1/2 yrs. Another of ours was a puppy mill survivor and 9 yrs old when we adopted. She lived for only another 1 1/2 yrs. The next was a kennel breeder and 7 yrs old - he was with us 5 1/2 yrs, and our current was 8 yrs old and has been with us for 5 yrs and a few months now. Thankfully she is very healthy except for failing eyesight. We wouldn't trade a minute of the time we spent with them and will do it all over again when the time comes.
Only words of wisdom would be - be patient with them while they adjust to their new home. We had one that pooped in each room of the house. We told him gently that was naughty - you have to go outside - would put him out. He went thru each room of the house - did his duty - was told no, outside again, and then never had another accident other than when sick in the house . They need to learn what is expected of them and it doesn't usually take long. They will worm their way right into your heart. Go for it!