my 1st was 23 months when ds2 was born. he was fine walking, we had a walking strap for a whiole that attached to his wrist and mine. there are plenty of options available for you tho, not ness a double buggy. there is the buggypod, a buggyboard, seat to go and also keeping ur eldest in the buggy and putting newbie in a sling/carrier for a while which is what we did
I have just bought an Out n about instep nipper - it is a side by side buggy and I haven't read a bad review of it anywhere, I thinki it is the slimest and lightests side by side on the market - it also folds fairly compact.
A friend of mine has a Phil and Teds and they do look great but I would say that her DS2 (6 months) is quite a big baby and I think she is concerned that he will soon grow out of the seat at the back before her DS1 is ready to give up the front seat and walk - plus they have a rubbish view!
dont have phil and ted but it is good, had my kids in one recently, 31/2 and 22mths and they were quite content, its dear thou.
some Jane models are quite nice.
my mc claren went to charity as soon as i could get it there, putting dd onto a buggy board at about 3, she still napped til then in the day so i could walk with both at a decent pace.
hated the mcc but i suppose it did the job.
saw a lady with a P&T in ELC today and the poor baby was screaming, he was practically at floor level and I was afraid a toddler was going to drop something on his head. Also she had huge amounts of things over the handle bar which looked like they could easily fall on him at any moment.
I had a graco tandem which was great for a newborn as he was totally enclosed in the back section. Not so good if your front passenger is very heavy and you do a lot of walking though. Luckily I just used it in shops and when ds was old enough he sat in the front which made the whole thing a lot lighter and easier to push. It wasn't perfect but only cost £90 and was really strong and sturdy.
I suppose it depends on how much walking you do and where you walk. I personally didn't like my buggyboard as it really hurt my back when pushing with it on and ds1 could easily jump off and run away.
I had the same dilemma but only 1.5 years between Mine. I have used a Maclaren twin traveller very slim for side by side, reasonably priced and suitable from birth. I got mine second hand from e-bay and as I reluctant double bugy owner have really found it very good!
My dd1 was 16 months when dd2 was born. I have a Phil and Ted and it is fab. I went to the Baby Show at the NEC at the weekend and I should have been on commission because of the number of people who kept on stopping me and asking all about it.
I've got a friend who has one and dd's both want to be in the rear seat! HTH