I know Nanuq knows this, but if anyone needs motivation to get active, have kids! Seeing the assumption that lots of physical activity is just a part of everyday life, that the car stays parked for days on end, and that the kids assume you'll get around by bike is so motivating to keep that lifestyle going it's great. For my kids to know that driving is something done rarely, and with a specific purpose, rather than part of a lifestyle is very rewarding.
Unfortunately, we bought an old small house close to my work so my commute is only 7km. If I extend the commute on the way home, I can get in 20km a day...nothing really unfortunately. I used to commute 40km a day...that was more productive.
Now, I have a beautiful close to 30 year old custom road bike updated to older Dura Ace STI stuff that I love...but haven't had a chance to ride too much, as I just ride my commuting beater.
More importantly, my wife and I have a fantastic Santana touring tandem with nice Ultegra and XTR stuff (yes on tandems you can effectively mix road and MTB parts) that with kids, we have yet to ride for years. Soon...we'll get the kids started riding the tandem...and then getting on their own bikes.
Big congrats on keeping it going John!! The bonding with your son at that age, doing stuff like that? Priceless. I am sooo looking forward to that. My kids are 75% younger.
Don't worry too much about the weight...worry about how you feel, and how strong you're getting. Muscle weighs more than fat!!