Goals from Anthony Straker and Freddy Eastwood secured the Shrimpers a third successive league win and their best start to a season in 23 years and that delighted Penney, celebrating his 49th birthday.
"It's still early days but we have to be pleased with the start we've made to the season and this was another good result and performance," said the former Doncaster manager.
"I'm 21 again and this was the perfect way to celebrate.
"It's the work rate of the players which is proving key at the minute and that made the difference again out there.
"It's not easy against 10 men and we proved that ourselves by winning after Barry Corr had been sent off at Hartlepool last weekend.
"But this was a good day and there were good performances all over the pitch.
"Daniel Bentley made a fantastic penalty save, Adam Thompson came in for his full debut and was excellent and it's all very positive.
"There's a long way to go though and we have to try and keep this going."